LlBTlxOiltX' 


UNIVERSITY  t>?^ 
DAVIS 


LTcncjaiA 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/aniparasiteshumanOOchanrich 


ANIMAL   PARASITES 

AND 

HUMAN   DISEASE 


BY 

ASA  C.  CHANDLER,  M.S.,  Ph.D. 

INSTRUCTOR    IN  BIOLOGY,    RICE    INSTITUTE, 
HOUSTON,    TEXAS 


SECOND   EDITION,   REVISED 


NEW  YORK 

JOHN  WILEY  &  SONS,  Inc. 

London:  CHAPMAN  &  HALL,  Limited 

1922 


LIBRARY 

UNIVERSITY  OF  CAIJFORNU 
DAVT'= 


Copyright,  1918,  1922 

BY 

Asa  C.  Chandler 


Stanbope  ipress 

F.    H.GILSON   COMPANY 
BOSTON.  U.S.A. 


To 

MY  MOTHER 

WHOSE   SELF-DENYING   LOVE   AND   UNFAILING 

DEVOTION  MADE  MY   SCIENTIFIC 

EDUCATION  POSSIBLE 


623 


PREFACE 

It  is  the  belief  of  the  writer  that  one  of  the  most  pressing  needs 
of  the  present  time  is  the  education  of  the  people  as  a  whole  in 
the  subjects  of  vital  importance  with  which  this  book  deals, 
and  an  increased  interest  in  this  field  of  scientific  work.  Scien- 
tists are  the  leaders  of  the  world,  and  should  constantly  endeavor 
to  keep  a  little  ahead  of  the  lay  population  who  follow  them. 
It  is,  however,  important  that  the  leaders  should  not  only 
blaze  the  trail,  but  should  make  it  sufficiently  easy  to  find  so 
that  the  followers  may  not  fall  too  far  behind.  In  the  intense 
fascination  of  exploring  the  trail,  and  the  eager  impulse  to  press 
on  to  newer  and  ever  newer  fields,  the  scientist  is  in  danger  of 
forgetting  the  handicaps  of  his  followers,  and  of  leaving  them 
hopelessly  in  the  rear.  Popular  ignorance  of  many  important 
facts  of  parasitology  and  preventive  medicine,  even  facts  which 
have  been  common  bases  of  operation  for  scientists  for  many 
years,  is  deplorable.  To  a  large  extent,  however,  the  scientists 
themselves  are  to  blame,  for  in  their  enthusiasm  for  discovery 
they  have  forgotten  to  make  it  possible  for  the  laity  to  reap  the 
benefits  of  their  investigations.  There  is  even  a  tendency  to 
belittle  the  efforts  of  those  workers  who  devote  their  energies 
toward  assisting  the  general  public  to  keep  in  touch  with  scientific 
progress.  A  book  or  paper  which  collects  the  work  of  others, 
models  it  into  a  connected  whole,  and  makes  readily  available 
what  before  was  widely  scattered  and  accessible  only  to  a  skilled 
"  library-prowler,'^  is  stigmatized  by  the  term  ''  mere  com- 
pilation." It  is  the  firm  belief  of  the  writer  that  this  is  not 
only  unjust  but  unwise.  No  less  mental  and  physical  energy, 
if  not  perhaps  even  more,  is  necessary  for  efficient  '*  mere  com- 
pilation "  than  for  the  addition  of  new  facts  to  scientific  knowl- 
edge, and  the  value  to  civilization,  which  must  be  the  ultimate 
criterion  by  which  all  scientific  work  is  judged,  must  be  equally 
as  great,  if  not  greater.  The  value  of  connecting  related  facts 
is  twofold:  it  helps  to  keep  the  world  in  general  somewhere 
nearly  abreast  of  the  times,  and  it  is  a  distinct  aid  to  further 

V 


Vi  PREFACE 

progress.  Having  the  courage  of  his  convictions  along  these 
lines,  the  writer  has  spent  much  time  which  he  might  other- 
wise have  spent  on  original  research  in  the  compilation  and  popu- 
larization of  the  subject  matter  of  this  book. 

It  is  the  aim  of  this  volume  to  present  the  important  facts  of 
parasitology,  as  related  to  human  disease,  in  such  a  manner  as 
to  make  it  readable  and  useful  not  primarily  to  the  parasi- 
tologist, but  to  the  public  health  and  immigration  service  officers ; 
to  the  physicians  who  are  concerned  with  something  more  than 
their  local  practice;  to  teachers  of  hygiene,  domestic  science  or 
other  subjects  in  which  health  and  preventive  medicine  are  im- 
portant; to  college  and  high  school  students;  to  the  traveler; 
and  to  the  farmer  or  merchant  who  is  interested  in  the  progress 
of  science  and  civilization.  It  is  the  hope  of  the  author  that 
this  book  may  not  only  be  a  means  of  making  available  for  the 
laity  facts  which  may  and  probably  will  be  of  direct  importance 
to  them  at  one  time  or  another,  but  that  it  may  also  be  instru- 
mental in  arousing  the  interest  of  more  students  in  this  branch 
of  science,  to  the  ultimate  end  of  enlisting  a  larger  number  in 
the  ranks  of  its  workers. 

No  attempt  has  been  made  in  the  following  pages  to  give 
detailed  descriptions  of  parasites,  or  to  go  further  into  their 
classification  than  seemed  necessary  to  give  a  correct  conception 
of  them.  Likewise  discussions  of  correct  scientific  names  and 
synonymy  have  been  entirely  omitted,  since,  important  and 
interesting  as  they  may  be  to  a  parasitologist,  they  are  of  no 
interest  to  the  lay  reader.  An  attempt  has  been  made  to  use 
scientific  names  which  are  most  generally  accepted  as  correct, 
except  that  in  cases  of  disagreement  between  American  and 
European  usage,  the  American  name  has  been  used.  In  cases 
where  some  other  name  than  that  adopted  in  this  book  has  been 
or  is  still  in  common  use,  it  is  given  in  parenthesis  to  afford  a 
clue  to  the  literature  associated  with  it. 

The  endeavor  to  avoid  repetition  in  the  discussion  of  certain 
parasites  in  one  chapter,  and  of  their  transmitting  agents  in 
another,  has  often  presented  difficulties,  since  some  facts  might 
equally  well  be  included  in  either  place.  As  far  as  possible 
these  facts  have  been  given  in  the  place  where  the  author  has 
felt  that  they  would  most  often  be  sought,  but  mistakes  have 
undoubtedly  been  made,  and  furthermore  what  one  reader  would 


PREFACE  VU 

search  for  under  "  malaria,"  for  instance,  another  would  seek 
under  ''  mosquitoes,"  and  vice  versa.  For  this  reason  frequent 
cross-references  are  given. 

As  far  as  has  seemed  advisable,  without  too  greatly  encumber- 
ing the  text  with  round-about  phrases,  scientific  terms  have  been 
omitted  or  if  used  have  been  explained.  It  is  difficult  to  keep 
constantly  before  one  the  unfamiliarity  with  even  everyday 
scientific  terms  of  many  readers  for  whom  this  book  is  intended, 
but  an  earnest  attempt  to  do  so  has  been  made. 

In  the  text  the  author  has  purposely  refrained  from  citing 
references  and  from  mentioning  more  than  a  few  names  of  in- 
vestigators. It  obviously  would  be  imj>ossible  to  give  refer- 
ences, or  even  to  mention  more  than  a  small  per  cent  of  the  thou- 
sands of  contributors  to  the  material  here  assembled  without 
making  the  text  cumbersome  and  unreadable,  especially  for  the 
readers  for  whom  the  book  is  especially  prepared.  Only  a  few 
of  the  leading  figures  in  the  history  of  each  group  of  parasites 
have  been  mentioned;  other  citations  would  have  meant  a 
more  or  less  arbitrary  selection  of  a  few  from  among  many, 
which  must  inevitably  result  in  injustice. 

For  similar  reasons  no  bibliography  is  given.  Instead,  the 
author  has  prepared  a  list  of  '^  Sources  of  Information  "  which 
includes  the  names  of  all  the  leading  periodicals  in  which  im- 
portant articles  on  parasitology  have  appeared  or  are  likely  to 
appear,  and  a  list  of  books  which  cover  all  or  a  portion  of  the  field 
of  parasitology  in  a  comprehensive  manner.  In  these  books 
will  be  found  bibliographies;  most  of  the  references  cited  in 
these  bibliographies  will  be  found  in  the  magazines  or  papers 
listed  in  ''  Sources  of  Information  "  and  this  list  will  aid  any- 
one interested  in  pursuing  the  subject  farther  to  keep  in  touch 
with  the  new  work  which  is  constantly  appearing.  The  author 
has  felt  that  more  real  value  would  attach  to  such  a  list  than  to 
a  list  perhaps  50  times  as  long  and  yet  inevitably  incomplete, 
containing  exact  references  to  particular  articles. 

The  illustrations,  with  two  or  three  exceptions,  have  been 
drawn  by  the  author  either  from  specimens  or  from  illustrations 
of  other  authors.  Pen  and  ink  drawings  have  been  used  con- 
sistently in  place  of  photographs  since  it  is  believed  that  such 
drawings,  if  carefully  done,  are  far  more  valuable  for  scientific 
purposes  than  are  photographs.     The  trained  eye  is  able  by 


vm  PREFACE 

voluntary  concentration  on  certain  parts,  and  inattention  to 
others,  to  see  much  more  than  can  a  camera,  which  has  no  such 
power  of  adjustment.  A  pen  and  ink  drawing  can,  therefore, 
represent  more  accurately  what  can  be  seen  by  the  eye  than  can 
a  photograph.  The  author  has  received  valuable  advice  re- 
garding the  illustrations  from  Mr.  A.  J.  Stover,  scientific  il- 
lustrator at  the  Oregon  Agricultural  College,  and  wishes  to  take 
this  opportunity  to  express  appreciation  for  it. 

Deep  appreciation  is  felt  for  the  invariable  willingness  with 
which  authors,  editors  and  publishers  of  scientific  papers  and 
books  have  given  permission  to  copy  illustrations.  Special 
mention  should  be  made,  however,  of  the  generosity  of  Sir 
Patrick  Manson  and  of  the  American  publishers  of  his  "  Tropical 
Diseases,"  Wm.  Wood  and  Co.;  of  Dr.  A.  Alcock,  author  of 
*' Entomology  for  Medical  Officers";  of  Professor  Wm.  A.  Riley 
and  Dr.  Johannsen,  authors  of  ''  A  Manual  of  Medical  Ento- 
mology," and  of  Dr.  A.  W.  Sellards,  who,  in  the  absence  of  Dr. 
Strong,  lent  photographs  taken  in  Peru  by  the  Harvard  School 
of  Tropical  Medicine.  The  illustrations  taken  from  the  journal 
Parasitology  have  been  especially  numerous,  and  mention  should, 
therefore,  be  made  of  the  unreserved  permission  to  use  them 
given  by  the  editor.  Professor  G.  H.  F.  Nuttall.  Many  illus- 
trations of  worms  have  been  taken  from  the  work  of  two  of  the 
real  pioneers  in  the  study  of  helminthology.  Professor  Karl 
Leuckart  of  the  University  of  Leipzig,  under  whom  many  of 
the  present  parasitologists  were  trained,  and  Professor  Arthur 
Looss  of  the  University  of  Cairo  in  Egypt.  It  is  a  high  tribute 
to  the  work  of  Professor  Leuckart  that  many  illustrations 
published  by  him  in  the  first  comprehensive  work  on  the  animal 
parasites  of  man,  in  1863,  are  still  the  best  available  ones  and 
will  be  found  reproduced  in  the  majority  of  modern  works  on 
the  subject. 

Particular  appreciation  is  felt  for  the  assistance  received  from 
three  publications  which  contain  reviews  of  current  literature 
in  particular  phases  of  medical  zoology,  namely,  the  Tropical 
Diseases  Bulletin,  which  reviews  practically  all  current  work 
on  protozoan  parasites  and  helminthology,  the  Review  of  Applied 
Entomology,  Series  B,  containing  abstracts  of  nearly  all  work 
on  medical  and  veterinary  entomology,  and  the  Journal  of  the 
American   Medical   Association,   which    gives   references    to   all 


PREFACE  ix 

articles  in  the  leading  medical  journals  of  all  countries,  and 
reviews  many  of  them.  Any  of  these  periodicals  will  be  lent 
by  the  Association  library,  at  the  average  cost  of  postage,  to 
any  member  of  the  Association.  These  three  publications,  on 
account  of  their  scope  and  thoroughness,  are  of  inestimable 
value  to  anyone  who  attempts  to  keep  pace  with  the  progress 
of  the  medical  sciences.  There  are,  however,  few  if  any  of  the 
journals  or  books  listed  under  "  Sources  of  Information  "  which 
have  not  been  drawn  upon  either  for  illustrations  or  infor- 
mation or  both.  All  of  these,  collectively,  have  made  this  book 
possible,  and  to  them,  and  to  the  workers  who  contribute  to 
them,  are  due,  therefore,  not  only  the  thanks  of  the  author  but 
also  the  thanks  of  everyone  who  may  profit  in  any  way  by  this 
book. 

The  writer  is  very  deeply  indebted  to  the  authorities  who  have 
been  kind  enough  to  read  the  manuscript,  and  who  have  freely 
given  the  benefit  of  helpful  suggestions  and  criticisms.  Pro- 
fessor Gary  N.  Calkins,  Professor  of  Protozoology  at  Columbia 
University,  Dr.  B.  H.  Ransom,  Zoologist  of  the  U.  S.  Bureau  of 
Animal  Industry,  and  Dr.  L.  0.  Howard,  Chief  of  the  U.  S. 
Bureau  of  Entomology,  have  helped  materially  to  round  off 
the  rough  corners,  and  fill  in  the  chinks,  of  the  sections  on  Pro- 
tozoa, "  worms,"  and  arthropods,  respectively. 

Hearty  thanks  is  also  due  my  wife,  Belle  Clarke  Chandler, 
for  the  invaluable  assistance  she  has  given  by  her  constant  and 
efficient  cooperation  in  the  editorial  part  of  the  work. 


TABLE  OF  CONTENTS 

Chap.  Pages 

I.  Introduction 1-11 

II.  Parasites  in  General 12-25 


PART  I.    PROTOZOA 

III.  Introduction  to  Protozoa 2&-37 

IV.  Spirochetes 38-73d 

Relapsing  Fever 42-48 

Syphilis 48-62 

Yaws 63-65 

Infectious  Jaundice 65-69 

Yellow  Fever 69-72 

Rat-bite  Fever 73-73a 

Other  Spirochaete  Diseases 73a-73d 

V.   Leishman  Bodies  and  Leishmaniasis 74-92 

Kala-azar 77-82 

Infantile  Kala-azar 82-84 

Oriental  Sore 84-88 

Espundia 89-92 

VI.   Trypanosomes  and  Sleeping  Sickness 93-114 

Sleeping  Sickness 98-108 

Chagas'  Disease 108-114 

VII.   Intestinal  Flagellates  and  Ciliates 115-127 

Bi-flagellate  Protozoa 117-118 

Multi-flagellate  Protozoa 118-125 

CiUates 126-127 

VIII.   Amebje 128-146B 

Intestinal  Amoebae 132-142 

Mouth  Amoebae 142-146B 

IX.  Malaria 147-167 

X.   Other  Sporozoa,  and  Obscure  or  Invisible  Parasites  168-194 

Coccidians 170-173 

Rhinosporidium 173-174 

Sarcosporidia 174-176 

xi 


XU  CONTENTS 

Chaf.  Pages 

Oroya  Fever 176-181 

Dengue 182-184 

Phlebotomus  Fever 184-185 

Rickettsia-like  Organisms 185-191 

Chlamydozoa 191-194 


PART  n.     "WORMS" 

XI.   Introduction  to  the  "Worms" 196-206 

XII.   The  Flukes 207-230 

Blood  Flukes 213-220 

Lung  Flukes 220-224 

Liver  Flukes 224-228 

Intestinal  Flukes 228-230 

XIII.  The  Tapeworms 231-253 

Family  Tseniidae 239-245 

Family  Dibothriocephalidae 245-247 

Larval  Tapeworms  in  Man 247-253 

XIV.  Hookworms 254-269 

XV.   Other  Intestinal  Roundworms 270-285 

XVI.   Trichina  Worms 286-297 

XVII.   FiLARi^  and  their  Allies 298-314 

Filaria  hancrofti 299-307 

Other  Species  of  Filariae 307-314 

XVIII.  Leeches 315-321 


PART  III.     ARTHROPODS 

XIX.   Introduction  to  Arthropods 322-330 

XX.   The  Mites 331-351 

Harvest  Mites 333-337 

Other  Occasionally  Parasitic  Species 337-341 

Itch  Mites 342-346 

Hair-foUicle  Mites 346-348 

Tongue-Worms 348-351 

XXI.  Ticks 352-369 

Ticks  and  Disease 359-363 

Other  Troublesome  Ticks 364-369 


CONTENTS  Xlll 

Chap.  Pages 

XXII.  Bedbugs  and  their  Allies 370-386 

Bedbugs 371-379 

Other  Parasitic  Bugs 379-383 

Remedies  and  Prevention 383 

Fumigation 383-386 

XXIII.  Lice 387-403 

XXIV.  Fleas .'. .  404-423 

XXV.   Mosquitoes 424-462 

Mosquitoes  and  Malaria 438-443 

Mosquitoes  and  Yellow  Fever 443-448 

Mosquitoes  and  Dengue 448-449 

Mosquitoes  and  Filaria 449-451 

Mosquitoes  and  Dermatohia 451-453 

Mosquito  Bites  and  Remedies  for  Them 453-455 

Control  and  Extermination 455-462 

XXVI.  Other  Blood-sucking  Flies 463-508 

Phlebotomus  Flies 466-473 

True  Midges  (Chironomidae) 473-477 

Blackflies  or  Buffalo  Gnats 478-484 

Gadflies  (Tabanid^) 484-490 

Tsetse  FHes 490-504 

Stable-FUes,  Stomoxys,  and  Their  AUies 504-508 

XXVII.   Fly  Maggots  and  Myiasis 509-528 

Blood-sucking  Maggots 511-513 

Maggots  under  the  Skin 513-519 

Myiasis  of  Wounds  and  of  Natural  Cavities  of  the  Body  519-523 

Myiasis  of  the  Intestine 523-528 

Sources  of  Information 529-533 


ANIMAL  PARASITES  AND 
HUMAN  DISEASE 


CHAPTER  I 
INTRODUCTION 


One  of  the  most  appalling  realizations  with  which  every  student 
of  nature  is  brought  face  to  face  is  the  universal  and  unceasing 
struggle  for  existence  which  goes  on  during  the  life  of  every 
living  organism,  from  the  time  of  its  conception  until  death. 
We  like  to  think  of  nature's  beauties;  to  admire  her  outward 
appearance  of  peacefulness;  to  set  her  up  as  an  example  for 
human  emulation.  Yet  under  her  seeming  calm  there  is  going 
on  everywhere  —  in  every  pool,  in  every  meadow,  in  every 
forest  —  murder,  pillage,  starvation  and  suffering. 

Man  often  considers  himself  exempt  from  this  interminable 
struggle  for  existence.  His  superior  intelligence  has  given  him 
an  insuperable  advantage  over  the  wild  beasts  which  might 
otherwise  prey  upon  him;  his  inventive  genius  defies  the  attacks 
of  climate  and  the  elements;  his  altruism,  which  is  perhaps  his 
greatest  attribute,  protects,  to  a  great  extent,  the  weak  and 
poorly  endowed  individuals  from  the  quick  elimination  which  is 
the  inevitable  lot  of  the  unfit  in  every  other  species  of  animal  on 
the  earth.  Exempt  as  we  are,  to  a  certain  extent,  from  these 
phases  of  the  struggle  for  existence,  we  have  not  yet  freed  our- 
selves from  two  other  phases  of  it,  war  and  disease.  We  have 
some  reason  for  hoping  that  after  the  present  world-wide  con- 
flagration of  war  has  burned  itself  out  and  its  ashes,  the  flesh  and 
bones  of  its  countless  victims,  have  disintegrated  and  disappeared 
from  view,  we  may  be  able  to  free  ourselves  from  the  probability 
of  ever  again  taking  part  in  or  witnessing  such  a  spectacle. 
That  the  helpless  bondage  in  which  we  were  once  held  by  disease 
will  never  again  be  our  lot,  we  can  say  with  more  assurance. 

1 


2  INTRODUCTION 

One  by  one  the  diseases  which  formerly  held  the  world  in  terror, 
or  made  parts  of  it  practically  uninhabitable,  are  falling  before 
the  onslaught  of  modern  science.  The  vast  majority  of  human 
and  animal  diseases  are  now  known  to  be  caused  by  organisms 
which  live  as  parasites  within  the  body.  In  all  but  a  few  cases 
these  organisms  are  now  definitely  known,  their  habits  under- 
stood, their  means  of  transmission  and  multiplication  worked 
out.  What  such  knowledge  means  to  the  human  race  can  hardly 
be  overestimated.  In  the  14th  century  Europe  was  swept  by  an 
epidemic  of  plague  which  destroyed  probably  one-fourth  of  her 
entire  population  —  something  like  25,000,000  people.  That 
a  similar  epidemic  would  have  swept  over  the  United  States 
in  the  present  century  had  it  not  been  for  modern  scientific 
knowledge  of  the  cause  and  means  of  transmission  of  plague, 
which  made  it  possible  to  nip  the  epidemic  in  the  bud  in  San 
Francisco  and  New  Orleans,  is  reasonable  to  believe.  In  the 
latter  part  of  the  19th  century  the  French  attempt  to  build  a 
canal  at  Panama  failed  dismally  after  a  stupendous  loss  of  life 
from  yellow  fever  and  malaria.  Shipload  after  shipload  of 
laborers,  engineers,  nurses  and  doctors  were  sent  to  the  great 
''  white-man's  graveyard,"  the  majority  to  succumb  in  a  few 
weeks  or  months  to  these  diseases,  at  that  time  uncontrollable. 
In  the  early  part  of  the  20th  century,  by  exterminating  malaria 
and  yellow  fever  on  the  Canal  Zone,  through  the  application  of 
the  knowledge  which  had  been  gained  in  the  intervening  years, 
the  Americans  made  possible  the  building  of  the  Panama  Canal. 
In  an  incredibly  short  time  this  zone  was  transformed  from  a 
veritable  pest  hole  to  one  of  the  healthiest  places  in  the  world, 
and  incidentally  the  "  conquest  of  the  tropics,''  previously  looked 
upon  as  a  more  or  less  hopeless  task,  was  shown  to  be  not  only 
possible  but  profitable.  To  quote  another  example,  through- 
out the  history  of  the  world  typhus  fever  has  hovered  like  a 
death  dragon  over  nearly  every  army  camp  ever  assembled, 
and  has  followed  in  the  wake  of  war  to  add  the  last  touch  of 
horror  and  desperation  to  the  inhabitants  of  the  countries  involved. 
In  the  present  unprecedented  war  only  those  countries  which  have 
not  kept  abreast  of  the  times  in  the  application  of  scientific  knowl- 
edge have  suffered  seriously  from  this  terrible  scourge.  Were  it 
not  for  the  application  of  modern  knowledge  the  horrors  of  the 
present  war  would  have  been  even  more  awful  than  they  are  now. 


IMPORTANCE  OF  PARASITIC  DISEASES  3 

A  decade  or  two  ago  a  child's  reader  contained  the  following 
lines : 

"  Baby  Bye, 
Here's  a  fly; 

We  will  catch  him,  you  and  I. 
How  he  crawls 
Up  the  walls, 
Yet  he  never  falls! 
I  believe  with  six  such  legs 
You  and  I  could  walk  on  eggs. 
There  he  goes 
On  his  toes, 
Tickling  Baby's  nose." 

What  a  contrast  to  this  attitude  toward  the  housefly  are  our 
present-day  fly-swatting  campaigns,  our  crusades  against  possible 
breeding  places  of  flies,  and  our  education  of  the  public  by  slogans, 
placards,  lectures,  magazine  articles  and  books  regarding  the 
filthy  habits  and  disease-carrying  propensities  of  this  selfsame 
housefly! 

But  let  us  not  think  for  a  moment  that  the  battle  is  won.  Not 
only  are  there  some  diseases  which  still  baffle  our  attempts  to 
cure  them  or  to  control  them,  or  even  to  understand  their  nature, 
but  those  which  we  already  know  how  to  control  are  by  no 
means  subdued.  Plague  continues  to  take  a  toll  of  life  in  India 
amounting  to  at  least  several  hundreds  of  thousands  a  year; 
malaria  even  today  destroys  directly  or  indirectly  millions  of 
people  every  year  and  more  or  less  completely  incapacitates 
many  millions  more;  syphilis  is  yet  one  of  the  principal  causes 
of  insanity,  paralysis,  still-births  and  barrenness  in  the  civilized 
world,  and  is  estimated  to  exist  in  10  per  cent  of  the  population 
of  the  United  States,  i.e.,  in  about  10,000,000  people;  hook- 
worms still  infect  and  render  more  or  less  imperfect  over  half  a 
billion  people  in  the  world ;  —  and  these  are  all  diseases  the  causes 
of  which  are  known,  the  means  of  transmission  recognized, 
methods  of  prevention  understood,  and  the  cure  of  which,  with 
the  exception  of  plague,  is  entirely  possible. 

It  is  evident  that  the  crying  need  of  the  present  time  is  not 
so  much  additions  to  our  knowledge  of  the  cause,  control  and 
prevention  of  diseases,  much  as  this  is  to  be  hoped  for,  as  it  is 


4  INTRODUCTION 

the  efficient  application  of  what  we  already  know.  Popular 
ignorance  of  diseases,  even  such  common  ones  as  malaria  and 
syphilis,  is  nothing  short  of  appalling.  This  ignorance  is  by 
no  means  confined  to  the  poorly  educated  masses;  it  is  wide- 
spread among  educated,  college-bred  people,  and,  piteous  as  it 
may  seem,  is  characteristic  of  many  professional  men,  among 
them  even  physicians  bearing  good  reputation.  There  are  a 
number  of  causes  for  this  unfortunate  condition.  Many  physi- 
cians of  the  old  school  have  been  so  busy  or  so  unprogressive 
that  they  have  never  attempted  to  add  to  or  modify  the  knowl- 
edge they  had  when  they  first  took  up  the  medical  profession  20 
or  30  years  ago;  people  with  erroneous  or  distorted  views  of 
things  publish  their  ideas  in  newspapers  or  magazines  as  authori- 
tative statements,  and  thus  unmeaningly  mislead  the  enormous 
number  of  people  who  swallow  such  newspaper  articles  without 
even  a  flicker  of  hesitation;  quack  doctors,  those  hellish  buz- 
zards who  prey  upon  the  innate  gullibility  of  the  greater  part 
of  the  human  race,  willfully  mislead  and  scatter  at  random  the 
seeds  of  misinformation  which  have  held  back  the  progress  of 
sanitation  and  health  to  a  pitiful  extent  and  have  borne  as  their 
fruit  sorrow,  misery  and  suffering;  and,  finally,  such  is  the 
conservativeness,  or  rather  imperviousness,  of  our  species  that 
a  new  idea  requires,  often,  not  decades  but  centuries  to  penetrate 
thoroughly  the  popular  mind.  It  is  nearly  60  years  since  Darwin 
brought  the  theory  of  evolution  into  serious  consideration  and 
showed  the  folly  of  belief  in  special  creation,  yet  it  is  no  exag- 
geration to  say  that  a  very  large  majority  of  people  at  the  present 
time  do  not  believe  in  evolution.  It  is  250  years  since  the  idea 
that  living  organisms  do  not  spontaneously  spring  into  exis- 
tence from  non-living  matter  was  first  promulgated,  and  nearly 
60  years  since  the  last  vestige  of  possibility  was  torn  from  the 
theory  of  spontaneous  generation,  yet  even  today  the  prev- 
alence of  such  beliefs  as  that  "  horse-hair  snakes  "  develop 
out  of  horse  hairs  in  water  is  nothing  short  of  astonishing.  It 
is  120  years  since  Jenner  proved  the  efficacy  of  vaccination 
against  smallpox,  yet  there  exist  at  the  present  time  numerous 
anti-vaccination  societies  whose  sole  purpose  is  to  denounce 
vaccination  as  an  impractical  and  illogical  proceeding.  How 
can  we  expect  popular  belief  in  the  mosquito  transmission  of 
malaria  which  was  demonstrated  only  20  years  ago! 


EXOTIC  DISEASES  O 

The  importance  of  the  study  of  parasites  in  connection  with 
human  disease  to  every  community  in  the  world  is  becoming 
more  and  more  obvious,  even  to  those  relatively  free  from  para- 
sitic diseases.  There  are  those  who  think  that  such  diseases 
as  kala-azar,  sleeping  sickness,  Oriental  fluke  infections  and 
many  other  local  or  "  tropical  "  diseases  are  of  no  vital  im- 
portance except  to  inhabitants  of  the  countries  directly  influ- 
enced or  to  travelers  through  these  countries.  That  the  im- 
portance of  such  parasitic  diseases  is  far  greater  than  this  is 
obvious  from  the  fact  that,  with  modern  facilities  for  com- 
munication and  with  the  extent  of  foreign  immigration  at  the 
present  time,  there  is  no  part  of  the  world  so  remote  that  the 
things  which  affect  it  may  not  also  affect  any  other  part  of 
the  world  if  conditions  are  suitable. 

There  is  probably  no  common  exotic  infection  which  is  not 
repeatedly  brought  into  the  United  States  through  immigration 
ports,  especially  in  ports  where  the  most  thorough  medical  in- 
spection of  immigrants  is  not  made.  In  the  port  of  San  Fran- 
cisco alone  over  50  per  cent  of  6428  Orientals  whose  faeces  were 
examined  in  the  course  of  a  little  over  two  years  were  infected 
with  hookworms,  each  one  capable  of  starting  a  new  center  of 
infection  in  a  previously  free  community.  According  to  Dr. 
BiUings  of  the  U.  S.  Immigration  Service,  during  the  "  Hindu 
Invasion  "  of  the  Pacific  Coast  of  the  United  States  in  1911, 
about  90  per  cent  of  all  arriving  Hindus  were  found  to  be  in- 
fected with  hookworms.  It  is  unfortunate  that  even  at  the 
present  time  a  considerable  proportion  of  arriving  Orientals 
cannot,  under  the  immigration  law,  be  subjected  to  medical 
examination. 

The  possibility  or  probability  of  other  diseases  becoming 
established  in  places  not  before  troubled  by  them  is  a  subject 
of  vital  importance  to  any  community  or  nation.  Some  of  them 
have  already  become  established  in  places  which  were  formerly 
free.  The  fact  that  acquaintance  with  these  exotic  diseases  is 
lacking  in  the  new  territory,  their  nature  not  understood,  means 
of  curing  them  unfamiliar,  and  means  of  prevention  of  spread 
unknown,  often  results  in  much  needless  suffering  and  loss  of 
life.  Furthermore,  many  infections  are  much  wider  in  distri- 
bution than  has  formerly  been  supposed.  To  cite  one  example, 
amebic  dysentery,  and  liver  abscess  which  is  often  the  sequel  to 


6  INTRODUCTION 

it,  occurs  over  the  greater  part  of  the  United  States,  yet  not 
only  are  the  people  unfamiUar  with  the  disease  and  its  cause, 
but  most  physicians  are  unacquainted  with  it  and  do  not  know 
how  to  diagnose  or  treat  it. 

The  history  of  modern  medicine,  so  far  as  infectious  diseases 
are  concerned,  is  nothing  more  nor  less  than  the  history  of  para- 
sitology in  its  broad  sense,  including  bacterial  and  fungous  para- 
sites as  well  as  animal  parasites.  Previous  to  the  beginnings  of 
our  knowledge  of  the  existence  of  microscopic  parasites,  and  of 
the  effects  produced  by  them,  nearly  all  diseases  were  interpreted 
as  visitations  from  angry  deities,  as  the  work  of  demons  or  as 
the  effect  of  supernatural  causes.  Such  ideas  are  still  prevalent 
in  those  parts  of  the  world  where  bacteriology  and  parasitology 
have  not  yet  penetrated. 

With  the  exception  of  the  superficial  acquaintance  which  the 
ancients  had  with  external  parasites  and  a  few  parasitic  worms, 
parasitology  began  about  the  middle  of  the  16th  century  when 
Fracastorio,  an  Italian,  published  his  belief  that  disease  was  due 
to  invisible  organisms  multiplying  within  the  body.  With  the 
invention  of  the  microscope  by  the  Dutch  lens-grinder,  Leeu- 
wenhoek,  actual  observation  of  microscopic  organisms  became 
possible,  and  this  famous  pioneer  in  science  observed,  in  1675, 
'^  animalculae  "  in  rain-water,  putrid  infusions,  saliva,  and 
diarrheal  excretions,  and  made  illustrations  of  them.  Based 
on  these  scanty  observations,  the  idea  that  all  diseases  were 
caused  by  these  ''  animalculse "  became  rampant  during  the 
succeeding  century.  In  1762  Plenciz,  a  physician  of  Vienna, 
apparently  with  the  tongue  of  a  prophet,  expressed  the  idea 
that  all  infectious  diseases  were  caused  by  living  organisms, 
that  there  was  a  special  "  germ  "  for  each  disease,  that  the 
incubation  period  of  diseases  was  due  to  the  time  necessary  for 
the  infecting  organisms  to  multiply,  and  that  the  organisms 
might  be  conveyed  through  the  air  as  well  as  by  direct  or  indirect 
contact.  In  the  18th  and  19th  centuries  there  was  much  con- 
troversy as  to  the  origin  of  ''  germs  "  and  the  possibility  of  their 
spontaneous  generation  from  putrefying  matter.  A  belief  in  the 
origin  of  living  organisms  only  from  pre-existing  organisms  was 
first  expressed  by  the  Italian  Redi,  in  1668,  but  scientific  proof 
of  it  came  much  later.  Experiments  by  Spallanzani  in  1769, 
Schulze  in  1836,  Schwann  in  1839,  Schroeder  and  von  Dusch  in 


HISTORY  7 

1854,  and  finally  Pasteur  in  1860  removed  one  by  one  the  last 
straws  to  which  the  sinking  theory  of  spontaneous  generation 
was  still  clinging. 

With  the  exception  of  tapeworms  and  some  intestinal  round- 
worms, one  of  the  first  worm  parasites  to  be  discovered  in  man 
was  Trichinella,  in  its  larval  stage  in  the  muscles,  this  discovery 
being  made  by  Peacock  in  1828.  The  hookworm  was  discovered 
by  Dubini  in  Italy  in  1838;  the  blood  fluke  and  the  dwarf  tape- 
worm by  Bilharz  in  Egypt  in  1851;  Filaria  (larvae)  by  Demar- 
quay  in  1863;  the  Chinese  human  liver  fluke  by  MacConnell 
in  India  and  MacGregor  in  Mauritius  in  1874;  the  adult  Filaria 
by  Bancroft  in  1876.  The  first  parasitic  protozoan  to  be  dis- 
covered and  recognized  as  such  was  the  ciliate,  Balantidium 
coll,  a  cause  of  dysentery,  discovered  by  Malinsten  in  1856. 
The  spirochaete  of  relapsing  fever  was  discovered  by  Obermeier 
in  1873;  the  dysentery  ameba  by  Losch  in  1875;  the  malaria 
parasite  by  Laveran  in  1880;  the  sleeping  sickness  trypanosome 
by  Forde  and  Button  in  1901 ;  the  Leishman  bodies  of  kala-azar 
by  Leishman,  and  independently  by  Donovan,  in  1903;  the 
spirochaete  of  syphilis  by  Schaudinn  in  1905. 

Knowledge  of  the  complicated  life  histories  characteristic  of 
many  parasites  practically  began  with  Zenker's  demonstration 
of  the  life  cycle  of  Trichinella  in  1860  and  Leuckart's  experimental 
proof  of  the  strange  life  cycle  of  the  beef  tapeworm  in  1861. 
In  1874  Weinland  discovered  the  snail  in  which  the  liver  fluke 
develops,  though  the  relation  of  flukes  to  molluscs  had  been 
previously  suspected.  In  1879  the  epoch-making  discovery  of 
the  role  of  the  mosquito  in  the  development  of  filarial  worms  was 
made  by  Manson  and  the  science  of  Medical  Entomology  was 
born.  This  discovery  has  been  so  far  reaching  in  its  results  and 
it  has  revolutionized  preventive  medicine  to  such  an  extent  that 
it  may  justly  be  looked  upon  as  marking  the  beginning  of  a  new 
era  in  the  history  of  preventive  medicine,  comparable  with  the 
discovery  of  the  germ  causation  of  disease.  One  of  the  first 
and  certainly  the  greatest  outcome  of  the  discovery  was  the 
discovery  by  Ross  in  1898  of  the  relation  between  mosquitoes  and 
malaria.  Other  important  discoveries  concerning  life  histories 
and  modes  of  infection  quickly  followed.  The  transmission  of 
trypanosome  diseases  by  tsetse  flies  was  discovered  by  Bruce  in 
1893;  the  relation  of  mosquitoes  to  yellow  fever  by  the  American 


8  INTRODUCTION 

Yellow  Fever  Commission  in  1900,  and  to  dengue  by  Graham 
in  1902;  the  relation  of  ticks  to  African  relapsing  fever  by  Button 
and  Todd,  and  independently  by  Koch,  in  1905;  the  relation 
of  ticks  to  spotted  fever  by  Ricketts  in  1906;  the  relation  of 
lice  to  typhus  by  Nicolle  and  his  fellow  workers  in  Algeria  in  1909, 
and  independently  by  Ricketts  and  Wilder  and  by  Anderson  and 
Goldberger  in  Mexico  in  the  same  year  (published  in  1910); 
the  relation  of  cone-noses  to  a  South  American  trypanosome 
disease  by  Chagas  in  1909;  the  life  history  of  blood  flukes  by 
Leiper  in  1914  and  1915;  and  the  r61e  of  crabs  as  second  inter- 
mediate hosts  of  lung  flukes  by  Nakagawa  in  1916. 

The  evolution  of  knowledge  concerning  the  treatment  of  para- 
sitic diseases  has  proceeded  along  two  distinct  lines,  one,  de- 
struction of  the  parasites  by  drugs  which  are  more  or  less 
specifically  poisonous  to  them,  the  other  by  vaccination  or  immu- 
nization. One  of  the  first  specific  drugs  known  was  quinine  for 
malaria.  The  use  of  cinchona  bark  from  which  quinine  in  its 
various  forms  is  manufactured  is  said  to  have  originated  with  the 
Indians  of  Ecuador,  and  to  have  been  introduced  into  Europe 
by  Spaniards  in  1642.  The  sulphate  of  quinine,  which  is  the 
form  of  the  drug  in  commonest  use  now,  was  first  used  in  1840. 
In  1880  Bozzolo,  an  Italian,  first  introduced  thymol  as  a  remedy 
for  intestinal  worms,  especially  hookworm,  and  this  has  been 
considered  a  standard  and  almost  specific  cure  for  hookworm 
until  within  the  last  two  years,  when  oil  of  Chenopodium  has 
been  substituted  for  it  to  a  large  extent.  The  next  specific  drug 
of  great  importance  to  be  discovered  was  salvarsan  for  spiro- 
chsetes,  discovered  by  Ehrlich  in  1905.  In  the  same  year 
atoxyl,  one  of  the  most  efficient  remedies  yet  discovered  for 
trypanosome  diseases,  was  discovered  by  Thomas.  Emetin  was 
discovered  to  be  a  specific  remedy  for  amebic  dysentery  by 
Rogers  in  1913  as  the  result  of  Vedder's  work  with  ipecac,  from 
which  emetin  is  manufactured.  In  1914  tartar  emetic,  pre- 
viously used  as  an  alternative  for  arsenic  compounds  (chiefly 
atoxyl)  against  trypanosomes,  was  discovered  by  Vianna  to  be 
a  wonderfully  efficient  specific  remedy  for  the  severe  South 
American  leishmaniasis,  and  was  subsequently  found  to  be  spe- 
cific for  all  Leishmania  diseases. 

Treatment  and  prevention  of  disease  by  immunization  has 
experienced  a  wonderful  development  in  the  past  35  or  40  years. 


IMMUNOLOGY  9 

Some  of  the  phenomena  of  natural  acquired  immunity  were  of 
course  familiar  even  to  the  ancients,  and  people  have  practiced 
for  centuries  exposing  themselves  to  diseases  at  convenient  times 
in  order  to  acquire  subsequent  immunity.  Jenner  in  1797 
devised  vaccination  with  cowpox  to  give  immunity  to  smallpox. 
It  was  not  until  1880  and  1881  that  Pasteur  discovered  the 
possibility  of  producing  immunity  by  inoculation  of  germs  arti- 
ficially rendered  harmless  or  relatively  harmless,  or  by  the  inocu- 
lation of  the  strained  excretions  of  the  bacteria  as  they  exist  in 
pure  cultures. 

From  Pasteur's  epoch-making  discoveries  has  arisen  in  the 
last  25  years  the  science  of  immunology.  Although  up  to  the 
present  time  the  successful  use  of  vaccinations  or  inoculations 
for  cure  of,  or  protection  from,  disease  germs  has  been  applied 
chiefly  to  bacterial  diseases,  the  same  principles  of  immunity 
apply  to  diseases  caused  by  animal  parasites  and  we  may  con- 
fidently expect  in  the  not  distant  future  a  great  extension  of  this 
relatively  new  field  of  medicine  to  diseases  caused  by  animal 
parasitesJ  It  has  already  been  applied  successfully  to  some 
spirochse^e  diseases,  and  to  some  trypanosome  diseases.  The 
difficulty  of  growing  many  animal  parasites  in  cultures  has  largely 
held  back  progress  along  this  line,  and  it  is  only  recently  that 
much  advancement  has  been  made.  Only  a  few  years  ago 
culturability  and  non-culturability  were  believed  to  be  dis- 
tinguishing characteristics  between  bacteria  and  Protozoa. 
Although  methods  for  growing  pure  cultures  of  bacteria  arti- 
ficially were  devised  and  used  by  Pasteur  in  1858,  and  greatly 
improved  by  Robert  Koch  15  or  20  years  later,  it  was  not  until 
1903  that  the  artificial  cultivation  of  trypanosomes  was  ac- 
complished by  two  American  workers,  Novy  and  MacNeal. 
In  1905  Rogers  in  India  succeeded  in  cultivating  the  Leishman 
bodies  of  kala-azar,  and  thus  established  their  relationship  to 
certain  flagellated  parasites  of  invertebrate  animals.  Since  then 
other  investigators  have  succeeded  in  the  cultivation  of  other 
parasitic  protozoans,  the  latest  important  accomplishment  along 
this  line  being  the  successful  cultivation  of  spirochsetes  by 
Noguchi  in  1910-12,  and  of  malarial  parasites  by  Bass  and  Johns 
in  1913.  As  yet  no  pathogenic  amebae  have  been  successfully 
cultured,  probably  due  to  their  dependence  on  the  presence  and 
action  of  certain  kinds  of  bacteria. 


10  INTRODUCTION 

Even  more  important,  if  anything,  than  abiHty  to  grow  para- 
sites on  artificial  cultures  in  order  to  experiment  with  them,  is 
ability  to  transplant  them  into  animals  which  can  be  experi- 
mented on.  Only  by  wholesale  animal  experimentation,  car- 
ried on  patiently  and  persistently,  for  years  sometimes,  could 
many  of  the  great  medical  victories  of  the  past  25  years  have 
been  won.  To  quote  from  MacNeal,  ''  The  importance  of  ex- 
perimentation upon  animals  in  the  development  of  our  knowledge 
concerning  disease-producing  microorganisms  can  hardly  be 
over-estimated.  .  .  .  Only  in  this  way  (by  the  use  of  animals 
in  considerable  numbers)  has  it  been  possible  to  discover  the 
causal  relation  of  bacteria  to  disease,  and  the  way  in  which 
diseases  are  transmitted.  .  .  .  The  inoculation  of  animals  also 
provides  accurately  controlled  material  for  studying  the  course 
and  termination  of  the  disease  as  well  as  the  gross  or  microscopic 
lesions  produced  by  it."  One  can  hardly  help  feeling  bitter 
against  those  well-meaning  but  misguided  individuals  who 
publicly  denounce  and  endeavor  to  minimize  the  unselfish  and 
tireless  labors  of  scientists  who  have  made  possible  the  allevi- 
ation and  prevention  of  so  much  human  misery  and  suffering. 
To  quote  from  Dr.  W.  W.  Keen  in  speaking  of  the  results  of 
Dr.  Flexner's  experiments  on  monkeys  and  guinea-pigs  with  one 
of  the  most  deadly  human  diseases,  cerebrospinal  meningitis: 
''  which  was  the  more  cruel.  Dr.  Flexner  and  his  assistants  who 
operated  on  25  monkeys  and  100  guinea-pigs  with  the  pure  and 
holy  purpose  of  finding  an  antidote  to  a  deadly  disease  and  with 
the  result  of  saving  hundreds,  and  in  the  future  thousands  on 
thousands  of  human  lives ;  or  the  women  who  were  '  fanned 
into  fury  '  in  their  opposition  to  all  experiments  on  living  animals 
at  the  Rockefeller  Institute  '  no  matter  how  great  the  antici- 
pated benefit?  ' 

"If  these  misguided  women  had  had  their  way,  they  would  have 
nailed  up  the  doors  of  the  Rockefeller  Institute,  would  have  pre- 
vented these  experiments  on  one  hundred  and  twenty-five  animals, 
and  by  doing  so  would  have  ruthlessly  condemned  to  death  for 
all  future  time  five  hundred  human  beings  in  every  one  thousand 
attacked  by  cerebrospinal  meningitis! 

''If  your  son  or  daughter  falls  ill  with  the  disease,  to  whom 
will  you  turn  for  help  —  to  Flexner  or  to  the  anti-vivisec- 
tionists?" 


SCIENTIFIC  PROGRESS  11 

It  is  inconceivable  that  any  anti-vivisectionist,  if  bitten  by  a 
rabid  dog,  would  not  hasten  to  be  given  a  Pasteur  treatment  to 
prevent  the  horrible  death  from  hydrophobia  which  would 
otherwise  almost  inevitably  result,  or  if  stricken  with  syphilis 
would  not  submit  to  treatment  with  salvarsan  in  order  to  pre- 
vent the  probable  ruin  not  only  of  his  own  life,  but  also  of  the 
lives  of  his  life-mate  and  of  his  unborn  children.  There  is  little 
thought  then  of  the  blood  of  the  monkeys,  guinea-pigs,  or  other 
animals  with  which  the  God  of  Knowledge  was  paid  to  make 
such  treatments  possible! 

The  discoveries  mentioned  in  this  brief  resum^  of  the  history 
of  parasitic  diseases  are  but  a  few  of  the  more  conspicuous  mile- 
stones on  the  path  of  progress  of  modern  medicine  as  related  to 
animal  parasites.  They  may  be  likened  to  the  posts  of  a  fence, 
while  the  hundreds  of  other  discoveries,  less  striking  in  them- 
selves, perhaps,  but  nevertheless  necessary,  correspond  to  the 
pickets.  The  posts  are  useless  without  the  pickets  as  are  the 
pickets  without  the  posts.  There  is  not  one  of  the  great  out- 
standing discoveries  in  the  field  of  parasitology  and  preventive 
medicine  which  could  have  been  made  without  the  aid  of  the 
less  illustrious  accomplishments  of  many  other  scientists.  Our 
present  ability  to  cope  with  and  control  disease  is  due  not  alone 
to  the  great  work  of  such  men  as  Manson,  Laveran,  Ross,  Pasteur, 
Koch,  Reed,  Schaudinn  and  Ricketts,  but  also  to  the  careful, 
pains-taking  work  of  thousands  of  other  investigators,  who,  often 
without  any  semblance  of  the  honor  and  recognition  which  they 
deserve,  and  perhaps  even  under  the  stigma  of  public  denuncia- 
tion, work  for  the  joy  of  the  working  and  feel  amply  repaid  if  they 
add  a  few  pickets  to  the  fence  of  scientific  progress. 


CHAPTER  II 
PARASITES  IN   GENERAL 

Definition.  —  According  to  the  Standard  Dictionary,  a  parasite 
is  a  living  organism,  either  animal  or  plant,  that  lives  on  or  in 
some  other  organism  from  which  it  derives  its  nourishment  for 
the  whole  or  part  of  its  existence.  In  the  following  pages  only 
those  parasites  which  belong  to  the  animal  kingdom  are  taken 
into  consideration.  The  vegetable  parasites,  chiefly  bacteria  and 
fungi,  are  dealt  with  only  incidentally. 

It  is  often  difficult  to  draw  a  sharp  line  between  parasites  and 
predatory  animals;  a  panther  is  unquestionably  a  predatory 
animal,  and  a  tapeworm  is  unquestionably  a  parasite,  but  a 
mosquito  or  horsefly  might  well  belong  in  either  category.  It  is 
usual  to  look  upon  an  organism  as  a  parasite  when  it  habitually 
preys  upon  other  organisms  which  are  superior  to  it  in  size  and 
strength.  In  accordance  with  this  view  all  animals  which 
habitually  prey  upon  man,  other  than  a  few  which  occasionally 
attack  and  overcome  him  by  superior  physical  prowess,  may  be 
considered  as  parasites  and  are  so  treated  here. 

The  state  of  dependence  of  an  inferior  on  a  superior  organism 
probably  arose  very  soon  after  life  began  to  differentiate  in  the 
world.  It  would  be  difficult,  if  not  impossible,  to  explain  step 
by  step  the  details  of  the  process  of  evolution  by  which  some  of 
the  highly  specialized  parasites  reached  their  present  condition. 
In  some  cases  parasitism  has  probably  grown  out  of  a  harmless 
association  of  different  kinds  of  organisms,  one  of  the  members 
of  the  association,  by  virtue,  perhaps,  of  characteristics  already 
possessed,  developing  the  power  of  living  at  the  expense  of  the 
other,  and  ultimately  becoming  more  and  more  dependent  upon  it. 

Kinds  of  Parasites.  —  There  are  all  kinds  and  degrees  of  para- 
sitism. There  are  facultative  parasites  which  may  be  para^ 
sitic  or  free-living  at  will,  and  obligatory  parasites  which  must 
live  on  or  in  some  other  organism  during  all  or  part  of  their  lives, 
and  which  perish  if  prevented  from  doing  so.     There  are  inter- 

12 


KINDS  OF  PARASITES  13 

mittent  parasites  which  visit  and  leave  their  hosts  at  intervals. 
Some,  as  mosquitoes,  visit  their  hosts  only  long  enough  to  get  a 
meal,  others,  as  certain  lice,  leave  their  hosts  only  for  the  purpose 
of  moulting  and  laying  eggs,  and  still  others,  as  the  cattle  tick, 
Margaropus  annulatus,  never  leave  except  to  lay  eggs.  There 
are  parasites  which  pass  only  part  of  their  life  cycles  as  para- 
sites; botflies,  for  instance,  are  parasitic  only  as  larvae,  hook- 
worms only  as  adults.  Some  organisms  Uve  parasitically  in  two 
or  more  different  animals,  often  of  widely  different  species,  in 
the  course  of  their  life  histories.  Such,  for  instance,  are  the 
filarial  worms  and  numerous  protozoan  parasites,  which  begin 
life  in  a  vertebrate  animal,  continue  it  in  an  insect,  and  finish  it 
in  a  vertebrate  again;  the  tapeworms,  which  begin  life  in  cer- 
tain vertebrates  and  finish  it  in  other  individuals  of  the  same  or 
different  species;  the  flukes,  which  begin  life  as  free-living  em- 
bryos, continue  it  through  two  or  more  asexual  generations  in 
particular  species  of  snails,  become  again  free-living  or  else 
parasitize  second  intermediate  hosts  such  as  crabs  or  fishes,  and 
finally  gain  admittance  to  their  ultimate  vertebrate  hosts. 
There  are  permanent  parasites  which  live  their  whole  lives,  from 
the  time  of  hatching  to  death,  in  a  single  host,  but  in  which  the 
eggs,  or  the  corresponding  cysts  in  the  case  of  Protozoa,  must  be 
transferred  to  a  new  host  before  a  second  generation  can  develop. 
Such  are  many  intestinal  protozoans  and  round  worms.  The 
final  degree  of  parasitism  is  reached,  perhaps,  in  those  parasites 
which  live  not  only  their  whole  lives,  but  generation  after  gener- 
ation on  a  single  host,  becoming  transferred  from  host  to  host 
only  by  direct  contact.  Such  are  the  scab  mites  and  many 
species  of  lice.  There  is  every  gradation  among  all  the  types  of 
parasites  mentioned  above,  and  a  complete  classification  of  para- 
sites according  to  mode  of  life  would  contain  almost  as  many  types 
as  there  are  kinds  of  parasites. 

It  is  sometimes  convenient  to  classify  parasites  according  to 
whether  they  are  external  or  internal.  External  parasites,  as 
the  name  implies,  are  those  which  live  on  the  surface  of  the  body 
of  their  hosts,  sucking  blood  or  feeding  upon  hair,  feathers,  skin 
or  secretions  of  the  skin.  Internal  parasites  live  inside  the  body, 
in  the  digestive  tract  or  other  cavities  of  the  body,  in  the  organs, 
in  the  blood,  in  the  tissues,  or  even  within  the  cells.  No  sharp 
line  of  demarcation  can  be  drawn  between  external  and  internal 


14  PARASITES  IN  GENERAL 

parasites  since  inhabitants  of  the  mouth  and  nasal  cavities  and 
such  worms  and  mites  as  burrow  just  under  the  surface  of  the 
skin  might  be  placed  in  either  category. 

Effects  of  Parasitism  on  Parasites.  —  The  effect  of  parasit- 
ism is  felt  by  both  parasite  and  host.  There  is  a  sort  of  mutual 
adaptation  between  the  two  which  is  developed  in  proportion 
to  the  time  that  the  relationship  of  host  and  parasite  has  existed. 
It  is  obviously  to  the  disadvantage  of  internal  parasites  to  cause 
the  death  of  their  host,  for  in  so  doing  they  destroy  themselves. 
It  is  likewise  to  the  disadvantage  of  external  parasites,  not  so 
much  to  cause  the  death  of  their  host,  as  to  produce  such  pain 
or  irritation  as  to  lead  to  their  own  destruction  at  the  hands  of 
the  irritated  host.  It  is  interesting  to  note,  for  instance,  that 
insects  which  depend  to  a  large  extent  on  man  for  food  have 
less  painful  bites  than  do  insects  which  only  occasionally  or  ac- 
cidentally bite  human  beings.  Together  with  a  softening  down 
of  the  effects  of  the  parasite  on  the  host,  there  is  a  concomitant 
increase  in  the  tolerance  of  the  host  to  the  parasite.  It  is  a  well- 
established  fact  that  a  disease  introduced  into  a  place  where  it 
is  not  endemic,  i.e.,  does  not  normally  exist,  is  more  destructive 
than  in  places  where  it  is  endemic.  The  variations  in  suscepti- 
bility to  parasites  are  directly  connected  with  the  subject  of 
immunity,  which  will  be  discussed  later.  An  organism  and  the 
parasites  which  are  particularly  adapted  to  live  with  it  may,  in 
a  way,  be  looked  upon  as  a  sort  of  compound  organism.  Those 
parasites  which  live  part  of  their  life  in  vertebrate  animals  and 
part  in  other  parasites  of  these  animals,  as  lice,  ticks  and  biting 
flies,  are  absolutely  dependent  for  their  existence  on  the  relation- 
ships of  the  vertebrates  and  their  parasites,  and  form  a  sort  of 
third  party  to  the  association. 

Aside  from  the  toning  down  of  their  effects  on  the  host,  para- 
sites are  often  very  highly  modified  in  structure  to  meet  the  de- 
mands of  their  particular  environment.  As  a  group,  parasites 
have  little  need  for  sense  organs  and  seldom  have  them  as  highly 
developed  as  do  related  free-living  animals.  Fixed  parasites  do 
not  need,  and  do  not  have,  well-developed  organs  of  locomotion, 
if,  indeed,  they  possess  any  at  all.  Intestinal  parasites  do  not  need 
highly  organized  digestive  tracts,  and  the  tapeworms  and  spiny- 
headed  worms  have  lost  this  portion  of  their  anatomy  completely. 
On  the  other  hand,  parasites  must  be  specialized,  often  to  a  very 


SPECIALIZATIONS  15 

high  degree,  to  adhere  to  or  to  make  theu*  way  about  in  their 
particular  host,  or  the  particular  part  of  the  host,  in  which  they 
find  suitable  conditions  for  existence.  Examples  of  speciali- 
zations of  external  parasites  are  the  compressed  bodies  of  fleas, 
permitting  them  to  glide  readily  between  the  hairs  of  their  hosts; 
the  backward-projecting  spines  of  fleas,  which  are  of  much  assist- 
ance in  forcing  a  path  through  dense  hair  by  preventing  any 
back-sUding;  the  clasping  talons  on  the  claws  of  lice;  the  barbed 
probosces  of  ticks;  and  the  tactile  hairs  of  mites.  In  these  same 
parasites  can  be  observed  marked  degenerations  in  the  loss  of 
eyes  and  other  sense  organs,  absence  of  wings,  and,  in  some 
cases,  reduction  of  legs.  Internal  parasites  are  even  more  pe- 
culiar combinations  of  degeneration  and  specialization.  They 
possess  all  sorts  of  hooks,  barbs,  suckers  and  boring  apparatus, 
yet  they  have  practically  no  sense  organs  or  special  organs  of 
locomotion,  a  very  simple  nervous  system,  and  sometimes,  as 
said  before,  a  complete  absence  of  the  digestive  tube. 

Still  more  remarkable  are  the  specializations  of  parasites,  in 
their  reproduction  and  life  history,  to  insure,  as  far  as  possible, 
a  safe  transfer  to  new  hosts  for  the  succeeding  generations. 
Every  structure,  every  function,  every  instinct  of  many  of  these 
parasites  is  modified,  to  a  certain  extent,  for  the  sole  purpose  of 
reproduction.  A  fluke  does  not  eat  to  live,  it  eats  only  to  re- 
produce. The  complexity  to  which  the  development  of  the  re- 
productive systems  may  go  is  almost  incredible.  In  some  adult 
tapeworms  not  only  does  every  segment  bear  complete  male 
and  female  reproductive  systems,  but  it  bears  two  sets  of  each. 
The  number  of  eggs  produced  by  many  parasitic  worms  may  run 
well  into  the  hundreds  of  thousands.  The  complexity  of  the 
life  history  is  no  less  remarkable.  Not  only  are  free-living  stages 
interposed,  and  intermediate  hosts  made  to  serve  as  transmitting 
agents,  but  often  asexual  multiplications,  sometimes  to  the  ex- 
tent of  several  generations,  are  passed  through  during  the  course 
of  these  remarkable  experiences. 

Effects  of  Parasites  on  Hosts.  —  The  effects  of  parasites  on 
their  hosts  are  almost  as  numerous  and  as  varied  as  are  the  kinds 
of  parasites,  and  vary  besides  with  the  susceptibility  of  the  in- 
dividual concerned,  his  physical  condition,  and  complication  with 
other  infections.  In  general  it  may  be  said  that  a  parasite  damages 
its  host  in  one  or  more  of  three  ways:    (1)  by  robbing  it  of  food 


16  PARASITES  IN  GENERAL 

which  has  not  yet  been  assimilated  and  utilized,  (2)  by  mechani- 
cally injuring  its  tissues  or  organs,  (3)  by  the  formation  of  ex- 
cretions or  "  toxins,"  which  act  as  poisons. 

The  first  method  of  damage  is  of  least  importance,  though  it 
is  obvious  that  the  amount  of  food  abstracted  by  some  parasites, 
e.g.,  large  tapeworms  which  may  reach  a  length  of  several  yards 
and  grow  at  the  rate  of  several  feet  a  month,  must  be  considerable. 

Much  more  serious  are  the  various  kinds  of  mechanical  injury 
to  tissues  or  organs.  This  damage  is  done  by  the  blood-sucking 
parasites,  such  as  hookworms,  flukes,  leeches  and  blood-sucking 
arthropods  and  the  tissue-devouring  forms,  such  as  dysenteric 
amebse,  malaria  parasites,  lung  flukes,  and  fly  maggots,  which 
may  not  only  devour  the  cells  of  the  body,  but  may  also  cause 
hemorrhages,  give  portals  of  entry  for  other  infections,  and  per- 
forate the  intestine.  Here  also  belong  the  obstructing  parasites, 
which  by  their  presence  block  bloodvessels,  as  do  subtertian 
malaria  parasites  or  blood  flukes;  stop  up  lymph  vessels,  as  do 
adult  filarial  worms;  or  partially  or  completely  close  up  such 
ducts  as  the  bile  duct  and  pancreatic  duct,  as  do  liver  flukes. 
There  are  also  parasites  which  damage  and  inflame  the  tissues  by 
boring  through  them,  as  does  Trichinella,  the  guinea-worm,  itch 
mites  and  fly  maggots. 

The  third  type  of  injury,  by  excretion  of  toxic  substances,  is 
done  to  some  extent  by  practically  all  parasites.  In  external 
parasites  the  damage  is  usually  done  by  an  excretion,  usually 
of  the  salivary  glands,  which  prevents  the  coagulation  of  blood, 
and  tends  to  inflame  the  tissues  with  which  it  comes  in  contact. 
In  the  case  of  internal  parasites  the  toxic  substances  are  prob- 
ably in  most  cases  the  waste  products  of  the  parasites,  voided 
into  or  absorbed  by  the  blood  or  neighboring  tissues.  In  many 
cases  these  toxins  have  specific  actions  on  particular  tissues  or 
organs,  so  that  parasites  in  one  part  of  the  body  may  do  their 
chief  damage  to  an  entirely  different  part.  Intestinal  worms, 
for  instance,  may  produce  considerably  greater  derangements 
of  the  blood  or  of  the  nervous  system  than  of  the  intestine;  the 
trypanosome  of  Chagas'  disease  produces,  by  means  of  toxins, 
specific  effects  on  the  thyroid  gland  and  gives  rise  to  the  symp- 
toms which  result  from  interference  with  the  gland,  even  though 
the  parasites  may  not  be  located  in  the  gland  itself;  the  bite  of 
certain  ticks  along  the  line  of  the  spinal  cord  or  on  the  middle 


INFECTION  AND  TRANSMISSION  17 

line  of  the  cranium  produces  a  specific  effect  on  the  motor  nerves, 
causing  paralysis,  presumably  through  the  action  of  salivary 
secretions  or  of  the  excretion  from  the  coxal  glands;  the  amebse 
of  pyorrhea,  or  the  bacteria  associated  with  them,  which  infect 
the  teeth  and  gums  give  rise  to  such  symptoms  as  rheumatic 
pains  in  the  joints,  anemia  and  a  disturbance  of  digestion.  In 
fact  it  may  be  said  that  a  very  large  number  of  diseases  or  ab- 
normal conditions  which  were  once  attributed  to  purely  physical 
causes,  such  as  imperfections  in  the  organization  of  the  body, 
or  which  have  been  accepted  merely  as  common  derangements 
of  the  human  machine  for  which  no  direct  cause  could  be  found, 
have  been  traced  to  the  effect  of  particular  parasites  located, 
perhaps,  in  some  unsuspected  part  of  the  body.  We  are  daily 
widening  the  scope  of  this  phase  of  pathology,  and  this  is  one  of 
the  main  reasons  for  the  present  important  position  of  parasi- 
tology among  the  medical  sciences. 

Modes  of  Infection  and  Transmission.  —  The  portals  of  entry 
and  means  of  transmission  of  parasites  is  a  question  of  the  most 
vital  importance  from  the  standpoint  of  preventive  medicine. 
In  the  past  few  decades  wonderful  strides  in  our  knowledge  along 
these  lines  have  been  made,  but  there  is  much  yet  to  be  found 
out. 

With  a  very  few  exceptions  animal  parasites  do  not  exist  in 
air  and  dust  as  do  many  vegetable  parasites,  although  some 
spirochaetes,  coughed  from  the  lungs  or  throat,  may  infect  other 
individuals  by  being  breathed  in,  and  the  granules  formed  by 
some  of  these  spirochetes  may  be  blown  about  with  dust  and 
thus  infect  in  the  manner  of  many  bacteria. 

Many  parasites  may  be  spread  by  direct  or  indirect  contact 
with  infected  parts,  e.g.,  the  spirochaetes  of  syphilis  and  yaws, 
the  mouth  amebse,  the  parasites  of  Oriental  sore,  itch  mites  and, 
of  course,  free-moving  external  parasites.  The  parasites  of  the 
digestive  system  and  of  other  internal  organs  gain  entrance  in 
one  of  two  ways.  They  may  bore  directly  through  the  skin  as 
larvse,  e.g.,  hookworm.  More  commonly  they  enter  the  mouth 
as  cysts  or  eggs,  e.g.,  dysentery  amebse  and  Ascaris;  as  larvae, 
e.g.,  pin  worm;  or  as  adults,  e.g.,  leeches.  Access  to  the  mouth 
is  gained  in  many  different  ways,  but  chiefly  with  impure  water, 
with  unwashed  vegetables  fertilized  with  "  night  soil,"  or  with 
food  contaminated  by  dust,  flies  or  unclean  hands.     The  para- 


18  PARASITES  IN  GENERAL 

sites  of  the  blood  or  lymphatic  systems  usually  rely  on  biting 
arthropods  (insects,  ticks  and  mites)  to  transmit  them  from  host 
to  host,  and  it  is  in  this  capacity,  i.e.,  as  transmitters  and  inter- 
mediate hosts  of  blood  parasites,  that  parasitic  arthropods  are 
of  such  vast  importance  (see  p.  322). 

Geographic  Distribution.  —  The  geographic  distribution  and 
dispersal  of  parasites  is  another  subject  which  has  received 
much  fruitful  attention  in  recent  years.  Parasites,  like  other 
organisms,  are  dependent  upon  certain  physical  conditions  of 
their  environment  in  order  to  thrive.  One  of  the  most  important 
limitations  on  the  dispersal  of  a  parasitic  disease  is  the  distri- 
bution of  suitable  hosts.  Some  parasites  can  live  with  ap- 
parently equal  vigor  in  a  large  number  of  hosts,  others  are 
confined  to  a  few  or  to  one  only.  A  double  limitation  is  placed 
on  parasites  which  require  two  hosts  in  order  to  complete  their 
life  history;  they  obviously  cannot  exist  beyond  the  territory 
where  both  hosts  exist  together.  The  local  as  well  as  geographic 
distribution  of  the  hosts  is,  of  course,  effective  in  limiting  the  dis- 
tribution of  the  parasites.  In  the  case  of  human  parasites,  the 
alternate  host  is  practically  the  only  limiting  factor.  The  geo- 
graphic distribution  of  human  sleeping  sickness  is  coincident 
with  the  distribution  of  certain  species  of  tsetse  flies;  the  distri- 
bution of  yellow  fever  nowhere  extends  beyond  the  range  of  a 
certain  species  of  mosquito;  Rocky  Mountain  spotted  fever  is 
geographically  limited  by  the  distribution  of  a  certain  species  of 
tick.  The  accidental  or  gradual  extension  of  the  range  of  one  of 
these  intermediate  hosts  is  likely  to  be  followed  by  an  extension 
of  the  disease  carried  by  it.  It  sometimes  happens  that  a  strain 
of  a  certain  parasite  establishes  itself  in  a  new  host,  thus  often 
greatly  extending  the  territory  which  it  affects,  and  this  is  a 
possibility  which  must  always  be  remembered  and  watched 
for.  The  trypanosome  of  Rhodesian  sleeping  sickness,  for  in- 
stance, is  very  possibly  a  race  of  Trypanosoma  hrucei,  which  is 
common  i^  domesticated  and  wild  game  animals  in  a  large 
portion  of  Africa.  Some  slight  alteration  in  the  nature  of  the 
parasite  has  made  it  possible  for  it  to  affect  human  beings  and 
thus  give  rise  to  a  new  disease.  A  somewhat  different  situation 
is  presented  in  the  case  of  Rocky  Mountain  spotted  fever,  the 
parasite  of  which  has  not  yet  been  discovered.  In  nature  ap- 
parently only  one  species  of  tick  acts  as  an  intermediate  host, 


NATURAL  IMMUNITY  19 

though  experimentally  other  ticks  may  become  infective.  There 
is  obviously  a  constant  possibility  of  the  establishment  of  the 
disease  in  other  species  of  ticks  and  thus  of  greatly  widening  the 
area  affected. 

Temperature  is  an  important  limiting  factor  for  those  parasites 
which  can  be  directly  influenced  by  it,  as  external  parasites  and 
those  which  are  free-living  during  a  part  of  their  existence. 
In  Mexico,  for  instance,  human  lice  are  entirely  absent  from  the 
hot  coastal  plains,  though  abundant  on  the  high  central  plateau. 
Hookworms,  which  are  free-living  in  their  young  stages,  are  con- 
fined to  a  broad  strip  around  the  tropical  and  warm  temperate 
portions  of  the  world,  and  occur  outside  these  limits  only  in 
short-lived  epidemics  during  the  warm  part  of  the  year.  Such 
parasites  as  bots  and  screw-worms  are  equally  exposed  to  the 
influence  of  climate,  since  they  are  free-Hving  in  the  adult  stage. 

Some  parasites  are  limited  by  other  environmental  conditions. 
In  the  case  of  such  intermittent  external  parasites  as  mosquitoes, 
biting  flies  and  cone-noses  it  is  obvious  that  not  only  tempera- 
ture and  humidity,  but  also  the  presence  of  suitable  breeding 
places  and  of  suitable  haunts  during  resting  times  must  be  neces- 
sary for  their  continued  existence.  Again,  the  local  distribution 
of  hookworms  is  determined,  to  a  large  degree,  at  least,  by  the 
nature  of  the  soil.  These  worms  abound  where  sandy  soil  occurs, 
but  are  rare  or  absent  where  there  is  only  limey  or  clayey  soil. 

Natural  Immunity.  —  As  has  already  been  pointed  out,  when 
a  parasite  is  introduced  into  a  region  where  it  was  previously 
unknown,  or,  what  amounts  to  the  same  thing,  new  hosts  are 
introduced  into  its  territory,  its  ravages  are  usually  worse  than 
in  places  where  it  has  been  endemic  for  a  long  time.  The  hosts 
and  parasites  of  a  given  region  come  to  a  point  of  equilibrium. 
The  host  becomes  largely  immune  to  the  effects  of  the  parasite, 
and  yet  harbors  it  in  sufficient  numbers  to  form  a  reservoir  for 
it,  and  thereby  acts  as  a  ''carrier."  In  some  cases  a  total  or 
partial  immunity  is  built  up  in  youth,  when  the  power  of  resist- 
ance to  parasitic  invasion  is  usually  high;  in  other  cases  it  is  the 
result  of  a  long  struggle  extending  through  many  generations. 
A  good  example  of  immunity  acquired  in  youth  is  found  in  the 
case  of  yellow  fever,  and  of  partial  immunity,  gained  through 
many  generations  of  adaptation,  in  the  case  of  hookworms  in 
negroes.     The  terrible  destruction  wrought  by  sleeping  sickness 


20  PARASITES  IN  GENERAL 

when  introduced  into  virgin  territory  in  Uganda  is  a  good  ex- 
ample of  the  results  which  may  come  from  such  an  introduction: 
in  districts  where  sleeping  sickness  has  existed  for  a  long  time 
the  death  rate  from  it  is  often  only  two  or  three  per  thousand, 
whereas  in  one  district  in  Uganda  the  population  was  reduced 
from  300,000  to  100,000  in  about  seven  years.  It  is  not  im- 
probable that  the  extinction  of  many  of  the  striking  types  of 
animals  which  dominated  the  earth  in  past  geologic  ages  may  have 
been  brought  about  by  the  sudden  appearance  of  or  exposure  to 
new  and  deadly  parasites;  only  those  forms  of  life  which  were 
able  to  resist  the  onslaught  of  the  parasites  remained  to  continue 
the  course  of  evolution. 

This  leads  us  to  a  consideration  of  the  remarkable  facts  of 
immunity.  The  power  of  the  blood  .of  vertebrate  animals  to 
react  against  invading  organisms  or  poisons  by  producing  sub- 
stances which  will  destroy  them  is  one  of  the  most  wonderful 
adaptations  in  all  the  realm  of  nature.  Though  the  details  of 
the  reaction  are  still  unknown,  the  chemical  substances  concerned 
still  undetermined,  and  many  of  the  influencing  factors  not  yet 
understood,  yet  the  progress  in  our  knowledge  of  the  mechanism 
of  acquired  immunity  has  taken  great  strides  since  Pasteur 
first  placed  the  development  of  immunity  on  a  scientific  basis 
not  quite  40  years  ago.  There  are  several  ways  in  which  the 
body  may  react  against  parasites.  One  method  is  by  the  ac- 
tivity of  the  large  free-moving  white  blood  corpuscles,  which 
actually  capture  and  devour  the  parasites  after  the  manner  of 
predaceous  protozoans.  This,  of  course,  can  be  done  only  in  case 
of  very  small  parasites,  such  as  bacteria  and  Leishman  bodies. 
Apparently  the  parasites  first  must  be  rendered  digestible  to  the 
white  blood  corpuscles  by  the  presence  of  an  accessory  substance 
in  the  blood,  known  as  an  opsonin.  This  substance  may  be 
thought  of  as  acting  like  a  sugar  coating  on  a  bitter  pill,  though  its 
effect  is  more  analogous  to  that  of  cooking  on  starch,  i.e.  increased 
digestibility.  Opsonins  are  normally  present  in  the  blood  but 
increase  as  a  reaction  to  the  presence  of  parasites.  The  degree 
of  development  of  opsonins  in  the  blood,  and  consequent  power 
of  the  white  blood  cells  to  capture  and  digest  parasites,  is  known 
as  the  opsonic  index. 

Sometimes  a  number  of  cells  work  together  to  form  a  capsule 
around  larger  parasites,  thus  walling  them  in  and  limiting  the 


IMMUNITY  REACTIONS  21 

sphere  of  their  activity;  this  occurs  in  the  case  of  Trichinella, 
filarial  worms,  larval  tapeworms,  fly  maggots,  etc.  It  occa- 
sionally happens  that  enzymes  are  developed  which  enable 
the  surrounding  cells  slowly  to  digest  the  parasites  thus  im- 
prisoned. 

More  important  than  these  physical  methods  by  which  the 
body  is  able  to  combat  parasites  are  the  biological  or  chemical 
methods.  One  of  the  most  wonderful  adaptations  in  the  animal 
kingdom  is  the  ability  of  tissues,  chiefly  the  blood  and  lymph  of 
vertebrate  animals,  to  react  against  invading  cells,  whether  they 
be  bacteria.  Protozoa,  blood  corpuscles  of  unrelated  animals,  or 
other  foreign  cells,  by  producing  substances  known  as  anti- 
bodies which  dissolve  these  cells,  or  cause  them  to  agglutinate, 
i.e.,  clump  together  and  lose  any  motile  power  they  may  have. 
The  living  body  is  also  able  to  destroy  the  poisonous  action  of  the 
excretions  or  toxins  of  parasites  by  the  development  of  protective 
substances  known  as  anti-toxins  which  form  some  sort  of  a  chemi- 
cal union  with  the  toxins.  Other  poisonous  products  are  ren- 
dered harmless  by  the  formation  of  "  precipitins  "  which  have 
the  special  property  of  uniting  with  the  toxic  substances  to  pro- 
duce insoluble  and  consequently  harmless  precipitates.  Pre- 
cipitins are  found  to  react  against  any  foreign  protein,  of  para- 
sitic origin  or  otherwise,  introduced  into  the  body.  There  is 
some  question  as  to  whether  immunity  reactions  against  animal 
parasites  are  exactly  comparable  with  those  against  bacteria, 
but  the  difference  is  probably  a  matter  of  degree  and  not  of 
fundamental  nature.  The  higher  organization  of  Protozoa  and 
of  other  animal  parasites  enables  some  of  them  to  react  against 
the  destructive  influence  of  the  serum  by  encysting,  or  by  form- 
ing spores,  and  thus  they  are  able  to  continue  their  existence  in 
spite  of  the  development  of  immunity,  though  in  very  limited 
numbers  and  with  limited  activity.  The  result  is  immunity 
without  sterilization;  in  other  words,  although  the  body  becomes 
more  or  less  completely  immune  as  far  as  suffering  from  the 
effects  of  the  parasite  is  concerned,  yet  the  parasites,  limited  in 
number  and  activity,  still  exist  within  it,  and  such  a  host  becomes 
an  "  immune  carrier."  With  few  exceptions  protozoan  diseases 
are  contrasted  with  bacterial  diseases  in  this  respect.  The 
gradual  development  of  anti-toxins,  precipitins,  etc.,  probably 
accounts  to  a  large  extent  for  the  relative  immunity  which  is 


22  PARASITES  IN  GENERAL 

developed  against  the  effects  of  intestinal  worms  as  well  as  against 
blood  and  tissue  parasites. 

Artificial  Immunity.  —  In  every  case  the  reaction  of  the  body 
against  parasites  invading  it  is  due  to  the  presence  of  some 
particular  substance  in  the  parasite  which  stimulates  the  body 
to  react  against  it.  This  substance,  whatever  it  may  be,  is 
called  an  antigen.  The  possibility  of  acquiring  immunity  with- 
out being  subjected  to  the  disease  lies  in  the  fact  that  the  antigen 
is  also  present  in  parasites  which  have  been  weakened,  by  one  of 
several  methods,  to  such  an  extent  as  to  be  powerless  to  cause 
the  usual  symptoms.  It  may  also  be  present  in  the  dead  para- 
sites or  even  in  the  strained  excretions  from  parasites,  as  obtained 
from  pure  cultures.  Vaccinations,  in  the  broad  sense,  are  inoc- 
ulations into  the  system  of  weakened  or  dead  parasites  or  of 
their  products.  The  body  reacts  against  the  harmless  antigen 
thus  injected  and  antibodies  are  built  up  just  as  if  the  disease  had 
been  actually  passed  through.  Antibodies  persist  throughout 
life  in  the  case  of  some  parasites,  for  several  years  in  others,  and 
for  only  a  short  time  in  still  others.  When  the  efficacy  of  the 
naturally  or  artificially  acquired  immunity  is  gone,  as  determined 
by  experimentation,  a  new  vaccination  must  be  submitted  to  in 
order  to  obtain  protection.  Thus  yellow  fever  immunity,  which, 
however,  cannot  be  artificially  produced,  normally  persists 
through  life;  smallpox  immunity,  as  acquired  by  vaccination, 
for  a  number  of  years;  and  artificially  acquired  typhoid  immunity 
for  about  three  years. 

Still  another  method  of  inducing  immunity  is  possible.  By 
rendering  some  susceptible  animal  very  highly  immune  to  a 
particular  parasite  by  repeated  inoculations  of  virulent  germs, 
its  serum  becomes  so  charged  with  antibodies  and  so  powerful 
in  its  action  against  the  particular  parasite  involved,  that  a  very 
small  quantity  of  such  serum  injected  into  another  animal  or 
man  is  sufficient  to  give  a  "  passive  "  immunity  —  passive  be- 
cause the  second  animal  has  taken  no  active  part  in  the  for- 
mation of  antibodies.  Such  immune  serum  has  been  found  of 
value  in  the  prevention  and  cure  of  certain  spirochsete  dis- 
eases as  well  as  a  number  of  bacterial  diseases.  It  has  the 
advantage  of  causing  no  discomfort  during  the  development  of 
the  immunity,  but  usually  is  of  shorter  duration  than  "  active  '^ 
immunity. 


ANAPHYLAXIS  23 

The  principles  of  artificial  immunity,  as  remarked  before,  have 
only  recently  become  understood,  but  the  science  of  immunology 
is  yearly  becoming  extended.  As  this  paper  is  being  written, 
experiments  with  preventive  and  curative  inoculations  against 
typhus  fever  and  against  infantile  paralysis  are  being  worked 
out  and  there  is  reason  to  hope  that  before  another  year  dawns 
these  two  terrible  diseases  may  be  added  to  the  already  consid- 
erable list  of  diseases  which  can  be  prevented  by  artificially 
produced  immunity.  Smallpox,  rabies,  cholera  and  diphtheria 
are  some  of  the  more  important  diseases  whose  guns  have  been 
unloaded  by  this  means.  While,  as  remarked  before,  compara- 
tively little  advance  has  been  made  in  the  application  of  the 
principles  of  immunity  to  animal  parasites,  yet  there  seems  to  be 
hope  that  in  the  coming  years  many  diseases  caused  by  Protozoa 
and  worms  may  be  conquered  by  further  knowledge  of  immu- 
nology. 

Anaphylaxis.  —  Mention  should  be  made  of  the  phenomenon 
of  anaphylaxis,  commonly  defined  as  an  exaggerated  suscepti- 
bility to  the  poisonous  effect  of  foreign  substances  in  the  blood, 
and  to  account  for  which  many  different  explanations  have  been 
proposed.  Based  on  extensive  experimental  work,  Novy  and 
De  Kruif  have  recently  (1917)  offered  a  new  and  revolutionary 
explanation  which  is  bound  to  be  of  far-reaching  significance. 
According  to  these  workers,  normal  circulating  blood  must  be 
presumed  to  contain  a  substance,  termed  the  "  poison  matrix," 
comparable  in  a  general  way  with  the  substance  in  the  blood 
known  as  fibrinogen.  The  latter  substance,  under  certain  condi- 
tions or  in  the  presence  of  certain  reagents,  is  transformed  into 
fibrin,  which  forms  a  network  of  fibers  in  the  meshes  of  which  the 
blood  corpuscles  are  caught,  and  by  means  of  which  the  clotting  of 
blood  is  effected.  The  same  reaction  which  leads  to  the  coagu- 
lation of  blood  also  transforms  the  poison  matrix  into  an  actively 
poisonous  substance  or  ''  anaphylatoxin,"  which  produces  the 
symptoms  commonly  known  as  anaphylaxis.  Furthermore,  it 
is  shown  that  the  transformation  of  the  poison  matrix  into 
anaphylatoxin  is  induced  or  accelerated  by  the  addition  of  al- 
most any  foreign  substance  to  the  blood,  e.g.,  bacteria,  trypano- 
somes,  tissue  cells,  agar,  peptone,  starch,  various  salts,  and  even 
distilled  water.  In  other  words  ''  the  circulating  blood,  through 
a  variety  of  agents,  may  be  changed  from  a  beneficial  and  harm- 


24  PARASITES  IN  GENERAL 

less  to  an  injurious  and  poisonous  state.  The  foreign  substance 
is  merely  the  trigger  which,  so  to  speak,  ignites  or  explodes  the 
charge  contained  within  the  blood  vessels."  In  the  case  of  so- 
called  "  specific  anaphylaxis,"  in  which  anaphylactic  poison- 
ing results  from  the  injection  of  particular  kinds  of  organisms 
or  toxins,  as,  for  instance,  the  shock  that  results  from  typhoid 
vaccination  of  a  person  already  immune  to  typhoid,  the  specific 
action  is  due  to  the  production  of  ordinary  anaphylatoxin  by  the 
interaction  of  an  antibody,  already  developed,  with  the  antigen 
which  produced  it.  To  cite  another  example,  it  has  been  shown 
that  injection  of  the  ground  bodies  of  ox  warbles  into  cattle 
which  have  been  infested  by  even  small  nunibers  of  these  mag- 
gots produces  an  anaphylactic  shock.  According  to  the  theory 
of  Novy  and  De  Kruif  this  would  be  explained  as  follows:  the 
presence  of  warbles  in  the  cattle  causes  the  production  of  anti- 
bodies in  the  blood.  Injection  of  warbles  places  large  quantities 
of  the  antigen  in  the  blood.  Interaction  of  antibody  and  antigen 
produces  a  substance  which  transforms  the  poison  matrix  al- 
ways present  in  the  blood  into  anaphylatoxin,  and  the  latter 
produces  the  symptoms  of  poisoning.  The  theory  has  recently 
been  advanced  that  the  severe  effects  of  the  bites  of  some  blood- 
sucking arthropods,  such  as  ticks,  mites  and  blackflies,  in  which 
the  first  attacks  are  much  milder  than  the  later  ones,  may  be 
in  the  nature  of  anaphylactic  reactions.  According  to  the 
theory  of  Novy  and  De  Kruif,  these  effects  would  be  produced 
by  the  formation  of  anaphylatoxin  as  the  result  of  an  interaction 
of  an  antigen  in  the  arthropod's  salivary  secretions  with  an  anti- 
body already  formed  in  the  bitten  individual. 

Novy  and  De  Kruif  point  out  the  possibility  that  substances 
inducing  the  formation  of  anaphylatoxin  may  be  produced  in  a 
normal  individual  by  some  pecuHarity  of  diet,  exposure,  obscure 
infections,  etc.,  and  while  the  amount  of  poison  thus  produced 
may  not  be  sufficient  to  cause  an  acute  anaphylactic  shock,  it 
may  be  sufficient  to  cause  a  subacute  or  chronic  form  of  poison- 
ing, leading  to  anemia,  cachexia,  etc.  The  significant  state- 
ment is  also  made,  and  is  apparently  well  supported,  that  a  con- 
siderable part  of  the  toxic  effects  of  infectious  diseases  is  in  all 
probability  due  to  the  formation  of  anaphylatoxin.  The  so- 
called  "  endotoxins  "  supposed  to  be  liberated  in  the  blood  by 
the  disintegration  of  bacteria  and  other  parasites   possibly  do 


TREATMENT  OF  ANAPHYLAXIS  25 

not  exist  as  specifically  toxic  substances.     They  may  be  sub- 
stances which  induce  the  formation  of  anaphylatoxin. 

Should  further  investigation  indicate  that  much  of  the  toxic 
effects  in  various  infectious  diseases  are  really  produced  by  a 
single  substance,  anaphylatoxin,  the  treatment  of  such  diseases 
will  be  revolutionized.  In  addition  to  the  giving  of  drugs  to  de- 
stroy the  infecting  organisms,  an  attempt  must  be  made  to  find 
an  agent  to  destroy  anaphylatoxin  in  the  blood  and  to  pre- 
vent its  further  formation.  Novy  and  De  Kruif  have  shown 
that,  in  test  tubes  at  least,  alkali  not  only  destroys  but  also  pre- 
vents the  further  formation  of  this  poison,  and  they  suggest  the 
use  of  alkalis  in  the  treatment  of  conditions  in  which  anaphylaxis 
may  be  playing  a  part.  Already  striking  results  have  been 
obtained  in  severe  cases  in  which  anaphylactic  poisoning  was 
believed  to  exist,  by  the  simple  administration  of  sodium  bi- 
carbonate or  sodium  acetate  in  doses  of  from  three  to  five  grams 
dissolved  in  about  a  half  a  glass  of  water,  given  at  intervals  of 
half  an  hour  to  an  hour.  The  object  of  this  is  to  raise  the  alka- 
linity of  the  blood  to  a  maximum  level  and  to  keep  it  there  during 
the  time  anaphylatoxin  is  being  formed.  If  confirmed  by  further 
investigation,  these  facts  must  be  looked  upon  as  among  the  most 
important  discoveries  in  the  entire  history  of  medicine,  and  how 
far  reaching  their  effects  may  be  cannot  now  be  even  guessed. 


PART  I  — PROTOZOA 

CHAPTER  III 
INTRODUCTION    TO    PROTOZOA 

Place  of  Protozoa  in  the  Animal  Kingdom.  —  It  is  usual  for 
zoologists  at  the  present  time  to  divide  the  entire  Animal  King- 
dom into  two  great  sub-kingdoms,  the  Protozoa  and  the  Metazoa. 
These  groups  are  very  unequal  as  regards  number  of  species. 
The  Metazoa  include  all  the  animals  with  which  the  majority 
of  people  are  familiar,  from  the  simple  sponges  and  jellyfishes, 
through  the  worms,  molluscs,  and  the  vast  horde  of  insects  and 
their  allies,  to  the  highly  organized  vertebrate  animals,  including 
man  himself.  The  Protozoa,  on  the  other  hand,  include  only 
microscopic  or  almost  microscopic  animals,  the  very  existence  of 
which  is  absolutely  unknown  to  the  average  lay  person.  Al- 
though some  Protozoa  are  readily  visible  to  the  naked  eye  there 
are  others,  such  as  the  yellow  fever  organism,  which  are  too  small 
to  be  seen  even  under  the  highest  power  of  the  microscope.  There 
is  no  question  but  that  in  point  of  numbers  of  individuals  the 
Protozoa  exceed  the  other  animals,  millions  to  one;  a  pint  jar 
of  stagnant  water  may  contain  many  billions  of  these  minute 
animals.  About  10,000  species  of  Protozoa  have  been  described, 
but  it  is  probable  that  there  are  thousands  more  which  are  not 
yet  known  to  science. 

The  distinction  between  the  Protozoa  and  Metazoa  is  based 
on  a  characteristic  which  is  of  the  most  fundamental  nature. 
The  Protozoa  are  animals  which  perform  all  the  essential  func- 
tions of  life  within  the  compass  of  a  single  cell.  The  Metazoa, 
on  the  other  hand,  are  many-celled  animals,  with  specialized 
cells  set  apart  to  perform  particular  functions.  A  protozoan 
cell,  even  though  sometimes  living  in  a  colony  of  individuals 
which  are  all  bound  together,  can  live  its  life  and  reproduce  its 
kind  quite  independently  of  any  other  cells,  having  in  itself  the 
powers  of  digestion,  respiration,  excretion  and  secretion,  sensi- 

26 


PROTOZOA  AND  BACTERIA  27 

bility,  motility  and  reproduction.  Most  metazoan  cells,  on 
the  other  hand,  are  so  specialized  for  particular  functions  that, 
if  separated  from  the  other  cells  with  which  they  are  associated 
in  the  body,  they  die  almost  immediately. 

The  very  fact  of  evolution  makes  it  difficult  to  draw  a  sharp 
and  fast  line  between  two  groups  of  organisms,  even  between 
such  fundamentally  different  groups  as  the  Protozoa  and  Meta- 
zoa.  There  are  always  border  line  exceptions  which  make  the 
work  of  the  systematic  zoologist  at  once  difficult  and  interesting. 
In  the  case  in  hand  there  are  colonial  Protozoa  in  which  all  of  the 
cells  are  not  exactly  alike,  but  have  at  least  the  beginnings  of 
specialization.  Some  protozoans,  such  as  the  intestinal  flagel- 
late Giardia  (or  Lamblia),  are  composed,  as  adults,  of  essentially 
two  cells  instead  of  one.  Such  animals  have  been  placed  by 
some  authors  in  a  distinct  order  to  which  the  name  Diplozoa 
(double  animals)  has  been  appHed.  On  the  other  hand,  in  the 
lowest  metazoans,  the  sponges,  there  is  only  very  limited  speciali- 
zation of  the  cells,  while  in  the  little-known  animals  which  are 
designated  as  "  Mesozoa  "  there  is  even  less  differentiation. 

The  distinction  between  Protozoa  and  Bacteria,  though  in- 
volving the  distinction  between  animals  and  plants,  is  much 
more  difficult.  As  we  descend  the  evolutionary  scale  of  plants 
and  animals  the  usual  distinctions  between  them  disappear  and 
it  becomes  difficult  if  not  impossible  definitely  to  place  certain 
species  in  either  the  plant  or  animal  kingdom.  The  possession 
of  a  distinct  nucleus  of  some  kind  and  some  type  of  sexual  re- 
production are  the  characteristics  which  usually  distinguish  the 
Protozoa  from  the  less  highly  organized  Bacteria.  Often,  how- 
ever, it  is  difficult  to  discover  sexual  phenomena,  or  to  interpret 
them  with  safety,  and  the  presence  or  absence  of  a  nucleus  is 
sometimes  equally  difficult  to  determine.  In  such  cases  pe- 
cuharities  in  life  cycle,  chemical  reactions,  staining  properties 
and  the  like  are  resorted  to  as  distinguishing  characteristics. 
Most  biologists  are  now  inclined  to  group  all  of  the  single-celled 
animals  and  plants,  including  Bacteria,  into  one  great  group 
known  as  the  Protista,  a  suggestion  first  made  by  Ernest  Haeckel. 
The  existence  of  such  groups  of  organisms  as  the  Spirochaetes 
and  the  Piroplasmata,  occupying  intermediate  positions  between 
Protozoa  and  Bacteria,  and  of  such  groups  as  the  chlorophyll- 
bearing  flagellates,  occupying  an  intermediate  position  between 


28 


INTRODUCTION  TO  PROTOZOA 


cytost. 


— ocs. 


sUa 


protozoans  and  green  algae,  makes  such  a  group  as  the  Protista 

appear  both  natural  and  convenient. 

Structure.  —  A  protozoan,  in  its  simplest  form,  conforms  to 

the  usual  definition  of  a  cell  —  a  bit  of  protoplasm  containing 

a  nucleus.  S  o  m  e- 
^^•>op.cU.  times  there  are  two 
or  more  similar  nuclei 
and  in  the  majority 
of  ciliates  there  are 
two  nuclei  which  dif- 
fer from  each  other 
(str.  rKn  ocs.)  both  in  form  and  func- 
tion, a  large  "  macro- 
nucleus  "  which  is 
associated  with  the 
ordinary  vegetative 
processes  of  the  cell, 
and  a  small  "  micro- 
nucleus  '*  which  ap- 
parently is  concerned 
only  with  sexual  re- 
production. In  some 
protozoans  nuclear 
material  is  extruded 
from  the  nucleus  itself 
into  the  protoplasm 
outside  where  it  floats 
about  in  the  form  of 

Fig.  1.     A  complex  ciliate,  Diplodinium  ecatidatum,  minUte     partlCles     or 

showing  highly  developed  organelles;  caec,  caecum  or  granules     known      aS 
rectal  canal;    cut.,  cuticle;    c.v.,  contractile  vacuole;      ,  ...        ,11,, 

cy top.,  cytopyge  or  cell  anus;  cytost.,  cytostome  or  cell  CnromiQia,  tne  latter 

mouth;    d.m.,   dorsal  membranelle;    ect.,    ectoplasm;  sometimes  having  the 
end.,  endoplasm;  mac.  n.,  macronucleus ;  mic.  n.,  mi-  ,  . 

cronucleus;  myon.  (str.  retr.  oes.),  myonemes,  strands  pOWCr,  Unuer   certam 

for  retracting  oesophagus;  oes.,    oesophagus;  or.    cil.,  cirCUmstanceS    of 

oral  cilia;  sk.  lam.,  skeletal  laminae.      X  750.     (After  „  .  ,    . 

Sharpe.)  formmg  new   nuclei. 

In  some  Protozoa 
there  is  no  nucleus  as  such,  though  the  essential  substance  of 
the  nucleus,  chromatin,  is  always  present,  but  in  scattered  par- 
ticles. 

The  protoplasm  of  a  protozoan  is  usually  more  or  less  clearly 


ect 


— end. 


cut. 


---caec. 


ORGANELLES 


29 


divisible  into  an  outer  and  inner  zone,  the  ectoplasm  and  endo- 
plasm,  respectively  (Fig.  1).  There  is  no  fundamental  difference 
between  these  two  layers  of  protoplasm,  merely  a  difference  in 
density.  The  ectoplasm  is  the  less  fluid  and  comparatively  clear, 
while  the  endoplasm  is  more  fluid  and  somewhat  granular.  The 
clearness  of  the  differentiation  between  ectoplasm  and  endo- 
plasm is  sometimes  useful  in  distinguishing  species  of  protozoans, 
especially  amebse.     The  ectoplasm  differs  from  the  endoplasm 


Fig.  2.  Types  of  organs  of  locomotion  in  Protozoa;  A,  Amasha  with  pseudo- 
podia;  B,  a  heliozoan  with  "axopodia";  C,  Bodo  with  free  flagella;  D,  Trypanosoma 
with  flagellum  attached  to  undulating  membrane;  E,  Choanoflagellate  with  flagel- 
lum  and  "collar";  F,  Pleuronema  with  cilia  and  undulating  membrane  formed  of 
fused  cilia;  G,  modes  of  insertion  of  cilia;  H,  Aspidisca  with  cirri.  (Figs.  F  to  H 
from  Calkins.) 

in  function  as  well  as  in  appearance.  The  ectoplasm  may  be 
likened  to  the  body  wall  and  appendages  of  higher  animals  while 
the  endoplasm  may  be  compared  with  the  viscera  or  inter- 
nal organs.  The  endoplasm  digests  food  and  has  the  power  of 
secretion  and  excretion,  while  the  ectoplasm  produces  the  vari- 
ous organelles  for  locomotion,  food  getting,  oxygen  absorption 
and  special  senses.  The  term  '' organelle  "  is  used  in  place  of 
"  organ  "  for  structures  which  are  only  parts  of  a  single  cell. 

Organelles.  —  The  organelles  contained  in  a  protozoan's  body 
may  be  many  and  varied.  Those  connected  with  movement  or 
locomotion  differ  in  different  groups  and  form  the  chief  charac- 
teristic on  which  the  usual  classification  into  Sarcodina,  Flagellata, 


30 


INTRODUCTION  TO   PROTOZOA 


Ciliata  and  Sporozoa  has  been  based.  The  simplest  type  of 
movement  is  by  means  of  simple  outfiowings  of  the  body  proto- 
plasm known  as  pseudopodia  (Fig.  2A).  This  is  the  common 
type  of  movement  in  one  of  the  four  great  classes  of  Protozoa, 
the  Sarcodina.  In  the  Flagellata  the  organelles  for  locomotion 
are  long  lashlike  outgrowths  known  as  flagella  (Fig.  2C),  from 
one  to  eight  or  more  in  number.  These  originate  from  a  parti- 
cle of  deep-staining  material  which  is  called  the  blepharoplast  or 
"  centrosome."  In  many  parasitic  flagellates  there  is  another 
deep-staining  body,  of  very  variable  size  and  form,  known  as  the 

parabasal  body  (also 
called  by  some  au- 
thors the  kineto-nu- 
cleus  or  blepharo- 
plast). Various  types 
of  parabasal  bodies 
are  shown  in  Fig.  3. 
This  body  usually 
arises  from  the  basal 
granule  and  often 
remains  connected 
with  it,  apparently 
being  associated  with 
the  function  of  loco- 
motion. From  the 
fact  that  it  seldom 
occurs  except  in 
parasitic  forms  it  is  possibly  a  special  adaptation  to  the  peculiar 
environment  encountered  by  such  animals.  By  some  protozo- 
ologists  the  parabasal  body  has  been  looked  upon  as  a  second 
nucleus  with  the  special  function  of  control  over  the  locomotor 
activities  of  the  animal,  and  it  has  been  thought  to  originate  by 
direct  division  from  the  main  nucleus,  but  there  is  no  conclusive 
evidence  for  this  view.  As  a  result  of  the  idea  that  the  parabasal 
body  is  of  nuclear  nature  some  workers  have  separated  those 
protozoans  which  possess  a  distinct  "  kineto-nucleus  "  from  those 
which  lack  it,  creating  the  order  "  Binucleata  "  for  them. 

In  the  Ciliata  the  organs  of  locomotion  are  in  the  form  of  cilia 
(Fig.  2F),  hairlike  outgrowths  which  are  shorter  and  more 
numerous   than   flagella   and   different   from   them   in   motion. 


Fig.  3.  Types  of  parabasal  bodies  (p).  A,  Leish- 
mania;  B,  Herpetomonas;  C,  Trypanosoma:  D,  Prowa- 
zekia  cruzi;  E,  Prowazekia  lacertce;  F,  Polymas;  G, 
Trichomonas  augusta. 


STRUCTURE  31 

Each  cilium  arises  from  a  tiny  deep-staining  dot  or  basal  granule 
(Fig.  2G),  which,  however,  is  probably  not  homologous  with  the 
blepharoplast  of  the  flagellates. 

Various  modifications  of  the  organelles  of  locomotion  occur, 
e.g.,  the  undulating  membrane  of  many  flagellates  (Fig.  2D), 
formed  by  a  delicate  membrane  connecting  a  flagellum  with  the 
body;  the  '^ collar"  of  the  choanoflagellates  (Fig.  2E);  the  mem- 
branelles  and  cirri  of  cilia tes  (Fig.  2F  and  H),  formed  by  the 
fusion  of  rows  or  groups  of  cilia;  and  the  axopodia  (Fig.  2B)  of 
some  Sarcodina  formed  by  the  development  of  supporting  rods 
in  pseudopodia,  thus  making  a  permanent  structure.  Of  quite 
a  different  nature,  but  none  the  less  organelles  of  movement,  are 
the  myonemes  (Fig.  1,  myo.),  found  in  many  Protozoa,  and  cor- 
responding to  the  muscle  fibers  of  Metazoa.  They  enable  the 
animals  to  twist  and  bend  their  bodies.  The  myonemes  are 
extremely  delicate  contractile  fibers  which  run  in  various  direc- 
tions in  the  ectoplasm  of  the  animal;  they  occur  most  commonly 
in  flagellates  and  ciliates.  In  some  protozoans  structures  have 
been  described  which  show  every  evidence  of  being  highly  or- 
ganized neuromotor  apparatus,  i.e.,  a  definitely  arranged  and 
organized  substance  having  a  nervous  control  over  the  contrac- 
tile fibers  or  myonemes  (Fig.  1,  mot.). 

Organelles  for  food-taking  occur  chiefly  in  the  flagellates  and 
ciliates.  Such  protozoans  may  have  a  "  cytostome "  or  cell 
mouth  for  the  ingestion  of  food  (Fig.  1),  and  a  "  cytopyge  "  or 
cell  anus  for  the  elimination  of  waste  matter.  They  may  also 
have  a  delicate  membranous  pharynx  (Fig.  1,  cjrtost.)  for  leading 
the  food  material  into  the  endoplasm,  and  food  vacuoles  into 
which  the  food  is  accumulated  and  in  which  it  is  circulated  in- 
side the  body.  In  some  protozoans,  namely  the  Suctoria,  a 
much  modified  group  of  ciliates,  there  are  developed  suck- 
ing tentacles  or  the  absorption  of  food.  In  others  there  are 
tiny  capsules  in  the  ectoplasm  containing  minute  threads 
which  can  be  shot  forth  when  stimulated,  and  used  either  to 
overpower  prey  or  for  protection  from  enemies.  For  the  ex- 
cretion of  waste  products  of  the  body  there  is  often  present  one 
or  more  contractile  vacuoles  (Fig.  1,  c.v.),  little  cavities  in  the 
protoplasm  of  the  body  which  expand  with  water  containing 
area  and  other  waste  matters  conducted  to  them  by  tiny  radiating 
canals,  and  which  periodically  contract,  forcing  their  contents 


32  INTRODUCTION  TO  PROTOZOA 

outside  of  the  cell,  sometimes  through  a  definite  excretory  pore. 
Sense  organs  in  the  form  of  pigment  spots  sensitive  to  light, 
and  outgrowths  sensitive  to  chemical  substances,  giving,  perhaps, 
a  sensation  comparable  with  taste,  are  present  in  some  species, 
especially  in  free-living  ones.  Various  organelles  serving  the 
function  of  a  skeleton  may  be  developed  in  the  form  of  a  tough 
cuticle,  a  chitinous,  calcareous  or  siliceous  shell,  a  chitinous  sup- 
porting rod  or  '^  axostyle  "  (Fig.  30,  axo),  or  even  a  complicated 
internal  skeleton  of  calcareous  material.  While  no  protozoan 
possesses  all  of  these  organelles,  many  possess  a  considerable 
number  of  them  and  exhibit  a  degree  of  complexity  and  or- 
ganization almost  incredible  in  a  single-celled  animal  which  is 
barely,  if  at  all,  visible  to  the  naked  eye. 

Physiology  and  Reproduction.  —  In  their  physiology  and 
manner  of  life  the  Protozoa  differ  among  themselves  almost  as 
much  as  do  the  Metazoa.  Some  ingest  solid  food  through  a 
cytostome  or  by  wrapping  themselves  around  it,  others  possess 
chlorophyll  and  are  nourished  in  a  typical  plant  manner,  and 
still  others  absorb  nutriment  by  osmosis  from  the  fluids  or 
tissues  in  which  they  live.  Acid  substances  corresponding  to 
the  gastric  juice  and  alkaline  substances  simulating  the  intesti- 
nal juices  may  be  present  in  the  protozoan  body,  often  localized 
in  definite  regions,  and  acting  upon  the  food  as  it  circulates  in 
the  food  vacuoles.  The  waste  material  either  is  voided  through 
a  cytopyge  or  is  left  behind  by  a  simple  flowing  away  of  the 
protoplasm.  Body  excretions  are  collected  by  the  contractile 
vacuoles  and  voided  by  them,  or  they  are  simply  passed  through 
the  body  wall  by  osmosis. 

The  multiplication  or  reproduction  of  protozoans  is  of  two 
quite  distinct  types,  an  asexual  multiplication,  more  or  less 
comparable  with  the  multiplication  of  cells  in  a  metazoan  body, 
and  sexual  reproduction,  comparable  with  a  similar  phenomenon 
in  the  higher  animals.  Several  common  asexual  methods  of 
multiplication  occur  amongst  protozoans,  namely,  simple  fission, 
or  division  into  two  more  or  less  equal  parts;  budding,  or  separa- 
tion of  one  or  more  small  parts  from  the  parent  cell;  and  multiple 
fission  or  sporulation,  a  breaking  up  into  a  number  of  individuals 
or  spores.  Multiplication  by  one  of  these  asexual  methods  may  go 
on  with  great  rapidity  for  a  long  time,  but  sooner  or  later  some 
process  at  least  remotely  resembling  sexual  reproduction  usually 


REPRODUCTION  33 

occurs.  While  such  a  process  has  not  been  observed  in  many 
protozoans,  it  presumably  occurs  in  all  under  certain  conditions. 
The  analogy  between  a  protozoan  life  cycle  and  a  metazoan 
life  cycle  has  become  understood  only  in  recent  years.  As  a 
result  of  the  painstaking  experiments  of  Calkins  and  other  pro- 
tozoologists,  it  is  now  usual  to  compare  the  entire  life  cycle  of  a 
protozoan  animal  from  one  sexual  reproduction  to  the  next, 
including  all  the  intervening  asexual  generations,  resulting  per- 
haps in  millions  of  individuals,  with  the  life  cycle  of  a  single 
metazoan.  According  to  this  view  the  asexual  reproduction, 
as  remarked  above,  is  comparable  with  the  multiplication  of 
cells  in  a  metazoan  body,  except  that,  instead  of  all  the  cells 
resulting  from  such  multiplication  remaining  together  and  be- 
coming specialized  for  particular  functions,  they  separate  and 
live  as  independent  individuals.  Just  as  the  cells  of  a  meta- 
zoan body  grow  old  after  a  variable  length  of  time  and  lose  their 
youthful  vitality  and  reproductive  power,  so  the  protozoan 
cells,  after  a  variable  number  of  multiplications,  gradually  lose 
their  vitality  and  reproductive  power.  In  the  metazoan  certain 
cells  have  the  power  of  renewing  their  waning  vitality  by  union 
with  a  cell  of  the  opposite  sex  (sexual  reproduction),  thus  be- 
ginning the  cycle  again.  In  the  protozoan  the  sexual  phenomena 
which  have  been  observed  are  believed  to  have  the  same  signifi- 
cance, and  there  is  evidence  that  at  least  in  some  Protozoa  the 
sexual  power  may  be  confined  to  certain  individuals  which  would 
then  be  comparable  with  the  sex  cells  of  the  metazoans.  Calkins' 
experiments  led  him  to  believe  that  in  Paramcecium,  a  common 
ciliated  protozoan  on  which  he  experimented  particularly,  old 
age  and  death  were  inevitable  after  a  variable  number  of  asexual 
generations  without  sexual  reproduction.  It  has  recently  been 
shown,  however,  that  when  conditions  of  life  are  perfect,  Para- 
mcecium may  continue  to  multiply  asexually  for  an  indefinite 
time.  Periodically,  however,  a  complete  reorganization  of  the 
cells  occurs  which  apparently  has  an  effect  similar  to  that  pro- 
duced by  sexual  reproduction,  the  animals  having  renewed  vi- 
tality for  many  generations.  This  remarkable  process,  named 
'*  endomixis,"  is  strikingly  analogous  to  parthenogenesis  (de- 
velopment of  unfertilized  eggs)  in  higher  animals.  Another 
analogy  is  that  under  unfavorable  or  adverse  conditions  sexual 
reproduction   replaces   endomixis,   just   as   in   such   animals   as 


34  INTRODUCTION  TO  PROTOZOA 

rotifers  and  small  crustaceans  it  replaces  parthenogenesis, 
though  either  endomixis  or  parthenogenesis  apparently  may  con- 
tinue indefinitely  with  conditions  favorable. 

Another  phenomenon  which  is  often,  though  not  always, 
associated  with  sexual  reproduction  is  encystment,  i.e.,  the  de- 
velopment of  an  impervious  enclosing  capsule  in  which  the 
delicate  protozoan  cell  is  able  to  resist  extremely  adverse  en- 
vironmental conditions,  such  as  very  high  or  low  temperatures, 
drouth,  presence  of  injurious  substances,  lack  of  oxygen,  etc. 
The  degree  of  protection  afforded  by  encystment  can  be  judged 
from  the  fact  that  encysted  amebae  exist  in  considerable  numbers 
on  the  sun-baked  sands  of  Egypt.  Encystment  may  take  place 
whenever  environmental  conditions  become  unfavorable,  or  as  a 
normal  stage  of  existence  following  sexual  reproduction,  thus 
being  comparable  with  the  impervious  shelled  eggs  of  many 
higher  animals,  or  sometimes  as  a  step  preliminary  to  some  form 
of  asexual  reproduction.  Nearly  or  quite  all  parasitic  protozoans 
which  are  not  transmitted  by  an  intermediate  host  adapt  them- 
selves for  passive  transfer  from  one  host  to  another  by  encystment. 

A  full  understanding  of  the  significance  and  limitations  of  the 
sexual  and  asexual  phases  of  the  life  histories  of  parasitic  Proto- 
zoa is  of  great  importance,  since  means  of  control  and  prevention 
often  hinge  on  these  points.  In  many  species  of  protozoan  para- 
sites a  different  host  is  required  for  the  sexual  portion  of  the 
life  xiistory  than  that  utilized  for  asexual  reproduction,  though 
this  is  not  true,  in  general,  of  the  intestinal  parasites.  Some 
species,  although  normally  utilizing  a  second  host  for  the 
sexual  reproduction,  are  apparently  able  at  times  to  pass  from 
host  to  host  without  the  intervention  of  an  intermediate  host  of 
different  species.  This  is  true,  for  instance,  of  the  sleeping 
sickness  trypanosome,  T.  gambiense,  which  is  normally  trans- 
mitted by  a  tsetse  fly,  Glossina  palpalis,  as  an  intermediate  host, 
but  which  is  thought  to  be  capable  of  direct  transmission  by 
sexual  intercourse  as  well.  It  is  interesting  to  note  also  that, 
according  to  observations  made  by  Gonder  on  trypanosomes 
(quoted  by  Nuttall),  characters  such  as  immunity  to  certain 
drugs,  acquired  by  protozoans  and  maintained  through  thousands 
'^f  asexual  generations  in  vertebrate  hosts,  may  be  blotted  out  at 
a  stroke  in  the  invertebrate  host  by  the  sexual  process  which 
presumably   occurs   there.     The    great   significance   of    this   is 


CLASSIFICATION  35 

evident :  one  of  the  difl&culties  connected  with  drug  treatment  of 
some  protozoan  diseases  is  the  power  of  the  protozoans  to  be- 
come immune  to  the  drug  when  given  in  doses  which  are  not 
destructive  to  the  host;  if  such  immunity  is  lost  during  trans- 
mission by  an  intermediate  host  there  is  no  danger  of  an  immune 
race  of  the  parasite  becoming  permanently  established. 

Classification.  —  It  is  little  wonder  that  such  a  varied  assem- 
blage of  single-celled  animals  as  constitutes  the  group  Protozoa 
should  be  difficult  to  classify.  It  is  obvious  that  these  simple 
animals  may  be  profoundly  modified  by  their  environment  and 
such  modifications  can  actually  be  seen  in  the  course  of  the  life 
history  of  many.  The  changes  in  form  undergone  by  a  trypano- 
some,  for  instance,  under  different  environmental  conditions  and 
at  different  periods  in  the  life  history  are  represented  in  Fig.  18. 

It  has  been  the  custom  among  zoologists  to  divide  the  Protozoa 
into  four  classes,  based  principally  upon  the  nature  of  the  organs 
of  locomotion.  These  classes  in  brief  are  as  follows:  Sarcodina, 
including  forms  with  pseudopodia;  Flagellata,  including  forms 
with  flagella;  Ciliata,  including  forms  with  cilia;  and  Sporozoa, 
a  heterogeneous  assemblage  of  parasitic  protozoans  which  as 
adults  have  no  organs  of  locomotion,  and  which  reproduce  by 
breaking  up  into  spores.  Though  other  classifications  have 
been  attempted,  the  above  system  is  the  one  generally  used. 
It  is  probable  that  it  is  not  in  all  respects  a  natural  classifica- 
tion, and  that  changes  in  it  will  be  made  with  increasing 
knowledge  of  Protozoa.  A  few  examples  of  the  difficulties  con- 
nected, with  this  classification  may  be  pointed  out.  There  are 
protozoans,  as  Craigia,  which  are  typical  Sarcodina  during 
part  of  their  life  cycle  and  typical  flagellates  during  another 
part,  and  some,  such  as  certain  soil  amebae,  which  readily 
change  from  one  phase  to  another  under  the  influence  of  varying 
environmental  conditions;  there  are  others,  as  Mastigamceba, 
which  exhibit  at  once  typical  pseudopodia  and  a  whip-like  organ 
which  can  only  be  regarded  as  a  flagellum;  there  are  species 
having  organs  in  every  way  intermediate  between  flagella  and 
cilia;  the  Sporozoa  contain  some  species,  such  as  the  malaria 
parasites,  Plasmodium,  which  during  a  part  of  their  life  have 
typical  pseudopodia  and  suggest  relationship  with  the  Sarcodina, 
others  which  show  striking  affinities  to  the  Flagellata,  and  still 
others  which  possess  coiled  projectile  threads  in  polar  capsules, 


36  INTRODUCTION  TO  PROTOZOA 

resembling  the  nematocysts  of  jelly  fishes.  Some  of  the  latter 
have  recently  been  elevated  to  the  rank  of  a  separate  class, 
Cnidosporidia,  by  the  German  parasitologist,  Braun.  Many 
other  difficulties  in  connection  with  the  classification  of  the 
Protozoa  as  outlined  above  could  be  cited,  but  since  no  more 
acceptable  classification  has  yet  been  proposed  this  classification 
is  followed  here. 

The  class  Sarcodina  consists  in  the  main  of  free-living  forms 
occurring  in  the  ocean,  fresh  water  and  soil.  Many  of  the  marine 
forms  are  furnished  with  calcareous  shells  which  are  largely  in- 
strumental in  building  up  chalk  deposits.  The  majority  of  the 
parasitic  species  belong  to  the  genus  EndamoBha. 

The  class  Flagellata  contains  some  of  the  most  primitive  as 
well  as  some  very  highly  specialized  kinds  of  animals.  Many  of 
the  free-living  forms  possess  chlorophyll  and  are  included  by 
botanists  in  the  Plant  Kingdom.  There  could  be  little  question 
about  their  vegetable  nature  were  it  not  for  the  fact  that  there  is 
every  gradation  between  those  which  are  typical  plants  in  form 
and  function  and  those  which  are  equally  typical  animals  in 
every  respect.  The  parasitic  species  are  all  of  distinctly  animal 
nature,  some  ingesting  and  devouring  solid  food,  others  absorb- 
ing food  by  osmosis.  With  the  flagellates  were  once  included, 
also,  the  spirochaetes  on  account  of  a  supposed  relationship  with 
the  trypanosomes,  but  this  theory  has  long  since  been  exploded, 
and  the  spirochaetes  are  now  usually  looked  upon  as  only  dis- 
tantly related  to  the  flagellates. 

The  class  Ciliata  is  least  important  of  the  four  classes  of  Pro- 
tozoa from  the  parasitologist's  point  of  view.  There  is  only 
one  species  of  ciliate,  Balantidium  coli,  which  is  common  and 
widespread  enough  and  pathogenic  enough  in  its  effects  to  deserve 
serious  consideration  as  a  human  parasite.  A  few  other  intestinal 
ciliates  have  been  discovered  in  man  but  they  are  of  little  im- 
portance. 

The  class  Sporozoa  contains  parasitic  forms  exclusively,  but 
fortunately  man  is  peculiarly  exempt  from  the  attacks  of  all  but 
a  few  species.  Among  the  few,  however,  are  included  the  ma- 
larial parasites,  which  rank  among  the  first  of  pathogenic  organ- 
isms as  regards  significance  to  the  human  race  as  a  whole.  It  is 
possible  that  the  undiscovered  parasites  of  such  diseases  as 
Rocky  Mountain  spotted  fever,  yellow  fever  and  dengue,  and 


IMPORTANCE  37 

the  parasites  of  obscure  nature  associated  with  smallpox,  rabies 
and  other  important  diseases  may  prove  to  be  members  of  this 
group. 

Importance.  —  Taken  as  a  whole  the  Protozoa  must  be  looked 
upon  as  a  group  of  organisms  of  prime  importance  as  human  para- 
sites. Although  Leeuwenhoek  discovered  the  existence  of  Pro- 
tozoa nearly  250  years  ago,  the  first  parasitic  species,  Balantidium 
coli,  was  discovered  by  Malmsten  in  1856,  only  61  years  ago. 
At  the  present  time  a  large  proportion  of  medical  practice  and 
disease  prevention  in  tropical  countries,  and  a  considerable  pro- 
portion in  all  countries,  depends  on  our  knowledge  of  the  habits 
and  life  history  of  parasitic  Protozoa,  nearly  all  of  which  has  been 
gained  in  the  last  35  years,  and  much  of  it  in  the  last  15  years. 
Almost  daily  new  discoveries  in  connection  with  disease-causing 
Protozoa  are  being  made;  there  are  few  branches  of  scientific 
research  which  offer  a  brighter  or  more  promising  field  of  endeavor 
for  students  at  the  present  time  than  the  investigation  of  patho- 
genic Protozoa. 


CHAPTER  IV 
SPIROCHETES 

General  Account.  —  On  the  vague  unsettled  borderline  be- 
tween Bacteria  and  Protozoa  there  is  a  group  of  organisms  which 
are  waging  a  frightful  war  against  human  life  and  health.  These 
organisms,  commonly  known  as  spirochsetes,  when  first  discovered 
were  supposed  to  be  of  bacterial  nature.  Later,  for  many  ap- 
parently valid  reasons,  they  were  thought  to  belong  to  the  Pro- 
tozoa, but  one  by  one  these  reasons  for  looking  on  them  as  animals 
rather  than  bacteria  are  falling  away  and  many  biologists  at  the 
present  time  relegate  them  to  their  old  place  among  the  Bacteria. 
They  still  serve  as  a  bone  of  contention,  however,  between  bac- 
teriologists and  protozoologists,  and  at  present  we  can  only  look 
upon  them  as  occupying  an  intermediate  position  between  the 
Bacteria  on  one  hand  and  the  Protozoa  on  the  other. 

Like  Bacteria  the  spirochsetes  lack  any  distinct  nucleus;  their 
multiplication  is  commonly  by  transverse  division,  although  the 
more  typically  protozoan  longitudinal  division  has  also  been 
claimed  for  them  by  some  investigators;  and  no  unquestionable 
conjugation  or  other  sexual  process  has  been  observed.  Like 
Protozoa,  on  the  other  hand,  some  of  the  spirochsetes  have  a 
membrane,  the  '^  crista,"  which  reminds  one  somewhat  of  the 
undulating  membranes  of  trypanosomes;  they  react  to  certain 
stains  and  chemicals  in  a  protozoan  manner;  and  they  multiply 
in  a  specific  intermediate  host  which  serves  as  a  means  of  trans- 
mission to  a  new  host.  Until  recently  it  was  believed  that  some 
spirochsetes  passed  through  a  distinct  phase  of  development  in 
such  intermediate  hosts  as  ticks  or  bedbugs,  but  some  doubt  has 
been  cast  on  this,  and  it  is  now  the  commonly  accepted  belief 
that  the  organisms  live  and  multiply  in  the  body  of  a  tick  or 
insect  just  as  bacteria  do  in  artificial  cultures,  without  going 
through  any  phase  of  their  life  history  which  does  not  at  least 
occasionally  occur  in  the  vertebrate  host. 

Spirochsetes  are  excessively  slender  threadlike  animals,  spirally 

38 


REPRODUCTION  39 

twisted  like  corkscrews.  They  are  very  active  in  movement, 
and  dart  back  and  forth  across  the  field  of  a  microscope  so 
swiftly  that  they  can  hardly  be  followed  by  the  eye.  The  move- 
ment is  apparently  by  wave  motions  passing  through  the  body, 
often  accompanied  by  a  rotation  of  the  body  in  corkscrew  fashion. 
Swiftly  moving  spirochsetes  show  many  small  waves  in  their 
bodies,  while  the  more  slowly  moving  ones  have  larger  and  more 
graceful  curls.  They  also  have  the  power  of  bending  their 
bodies  to  and  fro,  and  of  oscillating  while  attached  to  some  object 
by  one  end.  Spirochsetes  ordinarily  divide  by  a  transverse 
division  of  a  single  thread  into  two;  a  spirochsete  in  the  act  of 
such  division  can  be  seen  in  Fig.  6.  The  result  of  growth  in 
length  and  transverse  division  is  that  the  spirochsetes  of  any 
given  species  are  very  variable  in  size.  Often  individuals  can 
be  found  which  have  incompletely  divided  and  which  hang  to- 
gether in  long  chains.  Another  interesting  method  of  repro- 
duction in  spirochaetes,  the  details  of  which  have  been  worked  out 
largely  by  Fantham  and  his  students,  is  by  "  granule-shedding,'^ 
i.e.,  the  production  of  tiny  granules  by  a  breaking  up  of  the 
body  substance  inside  the  delicate  enclosing  membrane  into  a 
chain  of  round  ''  coccoid  bodies,"  resembling  coccus  forms  of 
bacteria  (Fig.  4).  These  minute  bodies  are  set 
free  either  by  a  disintegration  of  the  enclosing 
membrane  or  by  a  rupture  of  the  latter  at 
one  end.  The  elongation  of  the  granules,  the 
taking  on  of  the  sinuous  form  and  the  ultimate 
development  of  diminutive  spirochsetes  are  said 
by  several  investigators  to  have  been  observed 
by  them  in  living  cultures  of  these  organisms. 
It  is  probable  that  the  granule-shedding  occurs    ^         ff  •* 

at  regular  periods  in  the  life  of  spirochsetes,     ^         \        • 
and   that  it   is   comparable   to  the  process  of      Fig.4.  Spirochceta 
sporulat ion  in  malarial  parasites.     It  appears  to  duttoni,    showing 
be  particularly  associated  with  the  existence  in  P^'ocess    of   granule 
the  intermediate  host  if  there  is  one,  but  it  ^^'^^^^^^ ^^^  ^^ed- 

.,,,,..  ding.       (After    Fan- 

also  occurs  m  the  blood  of  the  vertebrate  host,  tham.) 
sometimes   apparently  in   preparation  for   the 
transfer   to   the   intermediate  host,  sometimes  as  a  protection 
against  adverse  conditions.     It  is  quite  likely  that  some  spiro- 
chsetes may  be  able  to  resist  atmospheric  drying  up  while  in 


40  SPIROCHETES 

the  granule  stage  and  may  thus  be  transmitted  in  dust  or  on  the 
bodies  of  flies.  Spirochoeta  bronchialis,  causing  a  form  of  bron- 
chitis, is  probably  transmitted  in  this  way. 

There  is  a  wonderful  variation  in  the  size  and  form  of  spi- 
rochsetes  and  also  in  their  mode  of  life.  A  few  species  are  free- 
Hving  and  of  very  large  size,  in  fact  almost  visible  to  the  naked 
eye  {^  mm.  in  length),  and  there  are  many  large  species  which 
live  as  harmless  commensals  with  various  mollusks.  The 
disease-causing  species  (some  examples  of  which  are  shown  in 


B 


)i>      )ii       }t      g 


Fig.  5.  Types  of  parasitic  spirochaetes.  A,  Sp.  duttoni;  B,  Sp.  novyi;  C,  Sp. 
pallida;  D,  Sp.  refringens;  E,  Sp.  balanitidis;  F,  Sp.  vincenti;  G,  Sp.  icterohemor- 
rhagicB.      X  about  1500.     (After  various  authors.) 

Fig.  5)  are  very  much  smaller,  often  being  so  delicate  and  slender 
as  to  be  hardly  visible  under  the  highest  powers  of  the  micro- 
scope. Not  all  the  small  spirochaetes  of  vertebrates  are  patho- 
genic however;  two  species  occur  almost  invariably  in  the 
human  mouth,  living  on  the  tartar  of  the  teeth  and  about  the 
roots  of  the  teeth,  and  yet,  normally  at  least,  cause  no  ill  effects. 
One  of  these  inhabitants  of  our  mouths,  Sp.  huccalis,  is  a  relatively 
short  blunt  species,  but  the  other,  Sp.  dentium,  is  excessively 
slender,  and  practically  indistinguishable  when  living  from  the 
spirochsete  of  syphilis.  Other  harmless  spirochaetes  occur  in 
various  stagnating  secretions  or  excretions  of  the  body,  about  the 
tonsils,  and  in  the  intestinal  mucus. 

Spirochaetes  and  Disease.  —  There  is  some  question  about 
how  many  distinct  human  diseases  are  caused  by  spirochaetes. 
The  mere  presence  of  spirochaetes  in  sores  or  diseased  tissue  is 
not  sufficient  reason  for  believing  that  they  are  the  direct  cause 
of  the  diseased  condition,  for,  like  many  bacteria,  they  are  often 
found  in  exposed  sores  which  are  known  to  be  due  to  other 
causes.  Spirochaetes  are  often  found  associated  in  sores  or  ulcers 
with  certain  kinds  of  bacteria,  and  both  bacteria  and  spirochaetes 


PATHOGENIC  SPECIES  41 

have  been  thought  by  some  workers  to  be  different  stages  in  the 
Hfe  history  of  a  single  organism. 

Spirochsetes  living  in  animal  bodies  have  a  strong  tendency  to 
localize  in  definite  parts  of  the  body  or  in  special  tissues.  The 
spirochsetes  which  choose  the  mouth,  the  teeth  or  the  digestive 
tract  as  a  habitat  have  already  been  mentioned.  Spirochoeta 
bronchialis  confines  itself  to  the  respiratory  tract,  causing  a  cer- 
tain type  of  bronchitis.  Sp.  schaudinni  localizes  in  skin  tissue, 
causing  ulcers,  in  certain  tropical  countries;  Sp.  iderohemorrhagice, 
although  probably  invading  many  parts  of  the  body,  especially 
affects  the  liver  and  kidneys;  the  spirochsetes  of  the  various  types 
of  relapsing  fever  confine  themselves  to  the  blood;  Sp.  pertenuis, 
the  cause  of  yaws,  produces  a  local  sore  followed  by  a  general  in- 
vasion of  the  body,  but  it  returns  to  the  skin  tissues  and  settles 
there;  Sp.  pallida,  of  syphilis,  is  able  to  produce  lesions  almost 
anywhere  in  the  body,  but  in  any  given  case  usually  attacks 
some  special  organ  or  tissue,  such  as  the  central  nervous  system, 
skin,  bones,  reproductive  system,  arteries,  etc.  Other  spiro- 
chsetes have  been  found  in  connection  with  many  different 
maladies,  for  instance,  Sp.  orientalis  in  '^  ulcerating  granuloma 
of  the  pudenda,"  an  ulceration  which  spreads  over  the  skin 
and  mucous  membranes  of  the  external  genital  organs;  Sp. 
vincenti  in  Vincent's  angina,  a  diphtheria-like  affection  of  the 
tonsils  and  throat;  Sp.  bronchialis  in  certain  types  of  bron- 
chitis; and  Sp.  balanitidis  in  balanitis,  an  erosion  or  ulceration 
of  the  glans  of  the  penis.  There  seems  to  be  more  or  less 
evidence  that  the  spirochsetes  found  in  connection  with  these 
diseases,  often  associated  with  bacteria  of  various  kinds,  may 
be  at  least  partially  responsible  for  them,  but  to  prove  this  is  a 
very  difficult  matter. 

In  general  the  diseases  caused  by  spirochsetes  may  be  divided 
into  three  groups.  The  first  of  these  is  the  type  in  which  the 
organisms  live  in  the  blood  and  cause  general  symptoms,  such  as 
fever,  spleen  enlargement,  and  anemia,  and  have  a  tendency  to 
cause  relapses.  Of  such  a  nature  is  rat-bite  fever  and  the  vari- 
ous forms  of  relapsing  fever.  Second,  there  is  the  type  in  which 
there  are  general  constitutional  symptoms  often  preceded  by  a 
local  lesion  of  some  kind,  followed  later  by  a  localization  of  the 
organisms  in  special  organs  or  tissues.  This  type,  characterized 
by  continued  or  remittent  attacks  rather  than  by  short  relapses, 


42  spirochtETES 

includes  such  diseases  as  syphilis,  yaws,  and  infectious  jaundice. 
The  third  type  is  that  in  which  occur  only  local  ulcerating  sores 
of  skin  or  mucous  membrane;  of  such  a  nature  are  the  other 
diseases  named  above. 

Relapsing  Fever 

In  every  continent  in  the  world,  with  the  possible  exception  of 
Australia,  there  occurs  a  form  of  relapsing  fever  caused  by  spiro- 
chsetes  in  the  blood.  In  Africa  it  ranks  next  to  malaria  and 
sleeping  sickness  as  a  scourge  of  that  disease-cursed  country. 
In  India  it  is  hardly  less  severe,  while  in  Eastern  Europe  and 
America  it  is  a  mild  disease.  The  cUnical  effects  of  these  various 
strains  of  the  disease  vary,  especially  in  the  number  and  duration 
of  the  relapses.  The  mode  of  transmission  also  varies  and  the 
parasites  are  apparently  distinguishable  and  are  therefore  given 
different  scientific  names.     The  African  spirochsete,  Spirochceta 

duttoni  (Fig.  6),  is  the  largest, 

being  about  16 /x  (y^^Vu  of  an 
inch)  in  length ;  it  has  only  two 
or  three  complete  spiral  turns 
and  is  quite  generally  admitted 
to  constitute  a  distinct  species. 
The  other  forms,  Sp.recurrentis 
of  Europe,  Sp.  novyi  (Fig.  5B) 
of  America,  Sp.  carteri  of  ori- 
ental countries,  and  perhaps 
still  others  in  other  regions, 
are  often  looked  upon  as  mere 
strains  or  varieties  of  Sp.  re- 
FiG.  6.    Spirochceta  duttoni  in  blood  of  cuvrentis,  which  was  the  One 

experimentally  infected  rat.     Upper  indi-    gj.g^      described.        These      SO- 
vidual  shows  transverse  fission.      X  1000.         ^^     i  •  j-cc 

called    species    differ    among 

(After  Novy  and  Knapp.)  i  i  •    n      •        •  i 

themselves  chietly  in  size,  and 
in  the  closeness  and  regularity  of  the  coils.  Each  type,  however, 
is  quite  variable  within  itself,  and  one  is  likely  to  be  misled  as 
to  size  by  the  hanging  together  of  several  individual  or  partially 
divided  spirochsetes  in  a  chain.  The  varying  symptoms  of  the 
different  types  of  the  disease  and  the  fact  that  immunity  to  one 
does  not  give  immunity  to  another  are  reasons  for  considering  the 
relapsing  fever  spirochaetes  as  constituting  several  species. 


RELAPSING  FEVER  43 

Although  relapsing  fever  was  known  to  physicians  over  a 
century  ago,  it  was  not  until  1873  that  Obermeier  discovered 
the  hitherto  unseen  agitator  which  causes  it;  he  made  his  dis- 
covery during  one  of  the  epidemics  which  spread  from  Russia 
over  Poland  and  Prussia. 

Many  great  epidemics  have  swept  Russian,  Austrian  and 
Balkan  cities.  Early  in  the  present  European  war  Serbia  was 
held  in  the  grip  of  an  epidemic  of  relapsing  fever  of  unusual 
severity  and  of  high  fatality.  In  Bombay  and  other  Indian 
cities  the  oriental  type  of  the  disease  is  nearly  always  present, 
and  it  sporadically  appears  in  various  parts  of  North  Africa, 
China  and  Japan.  In  tropical  Africa  it  occurs  over  a  large 
part  of  the  continent  occupied  by  the  tick  which  transmits  it. 
It  is  also  probably  widely  distributed  throughout  Mexico  and 
Central  and  South  America.  In  the  United  States  it  occurs 
chiefly  as  irregular  epidemics  among  immigrants.  Just  recently 
a  small  epidemic  occurred  in  Colorado. 

Transmission.  —  In  Africa,  where  the  disease  is  commonly 
known  as  "  tick  fever,"  it  was  thought  for  a  long  time  to  be  the 
result  of  the  poisonous  nature  of  the  bite  of  a  common  house- 
infesting  tick,  Ornithodorus  mouhata  (see  p.  360,  and  Fig.  155). 
This  tick,  which  inhabits  the  huts  of  natives  throughout  Central 
Africa,  is  the  chief  if  not  the  only  transmitter  of  the  Central 
African  relapsing  fever  spirochaete,  Spirochceta  duttoni.  It  can 
infect  both  man  and  monkeys  by  its  bite. 

It  has  been  shown  that  the  spirochsetes  can  live  for  a  long  time 
in  the  ticks  though  they  apparently  disappear  from  the  digestive 
tract  after  nine  or  ten  days,  many  of  them  penetrating  to  the 
blood-filled  body  cavity  while  still  in  the  spirochaete  form.  Leish- 
man  found  that  the  spirochaetes  break  up  into  a  series  of  tiny 
granules  which  penetrate  many  of  the  organs  of  the  tick,  in- 
cluding the  ovaries  and  eggs.  When  the  ticks  are  exposed  to  a 
temperature  of  95°  F.  for  a  few  days  the  spirochaetes  reappear. 
The  ticks  may  remain  infective  a  year  and  a  half  after  feeding 
on  an  infected  person  though  frequently  fed  on  clean  blood  in 
the  meantime,  and  a  single  tick  may,  therefore,  infect  a  number 
of  people.  By  means  of  the  granules  the  spirochaetes  may  be 
passed  on  to  a  second,  or  even  to  a  third,  generation  of  ticks 
through  the  eggs.  Young  ticks  reared  in  the  laboratory  from 
infected  parents  have  been  found  capable  of  transmitting  the 


44  SPIROCHETES 

disease.  Indeed,  the  tiny  unfed  nymphs  are  very  infective,  and 
on  account  of  their  small  size  are  particularly  dangerous  since 
they  are  not  easily  detected.  The  ticks  do  not  usually  transmit 
the  parasites  by  means  of  the  beak  but  deposit  a  bit  of  infected 
excrement  beside  the  wound  they  make;  from  here  the  spiro- 
chsetes  make  their  way  into  the  blood,  aided  by  the  scratching 
which  follows  the  tick  bite.  However,  when  the  tick  is  kept 
for  a  few  days  at  a  temperature  of  95°  F.  the  salivary  glands  as 
well  as  nearly  all  other  organs  become  infective,  and  the  disease 
may  then  be  transmitted  in  the  usual  insect  manner,  by  injection 
with  saliva.  The  relapsing  fever  of  Abyssinia  and  Somaliland 
is  transmitted  by  a  closely  allied  tick,  Ornithodorus  savignyi. 
African  tick  fever  is  said  to  have  been  imported  into  Persia, 
where  it  is  transmitted  by  0.  tholosani.  The  complete  life  cycle 
of  Spirochoeta  duttoni  is  shown  diagrammatically  in  Fig.  7. 

The  other  types  of  relapsing  fever  spirochetes  do  not  appear 
to  have  such  definite  and  invariable  transmitters.  Nicolle  and 
his  fellow  workers  have  shown  that  in  Algeria  the  head  and 
body  lice  are  undoubtedly  the  means  of  spreading  the  disease. 
In  experimental  work  they  have  shown  that  there  is  a  rapid  tem- 
porary disappearance  of  the  spirochsetes  from  the  body  of  the 
louse  after  they  have  been  sucked  with  blood  from  an  infected  per- 
son; during  this  time  they  are  presumably  in  the  granular  stage. 
After  about  eight  days  the  spirochsetes  reappear  and  are  abundant 
in  the  body  cavity  of  the  louse  for  some  12  days  before  they 
finally  disappear  for  good.  The  lice  are  infective  while  spiro- 
chetes are  present  in  their  usual  form,  and  also  just  before  they 
reappear  at  the  end  of  eight  days.  It  is  by  crushing  the  louse 
and  allowing  the  juices  from  its  body  cavity  to  contaminate  the 
wound  that  infection  is  obtained. 

In  experimental  work  in  Algeria  a  man  experimented  upon 
was  bitten  several  thousand  times  by  infected  lice  without  con- 
tracting the  disease,  but  one  louse  crushed,  and  the  body  fluids 
placed  on  the  conjunctiva,  caused  the  disease  to  develop.  The 
same  result  would  undoubtedly  have  occurred  if  the  crushed 
louse  had  come  in  contact  with  a  wound  of  the  skin. 

In  some  cases  the  spirochetes  are  transmitted  through  the 
eggs  to  the  next  generation  of  lice,  just  as  in  the  case  of  ticks  and 
the  African  disease.  The  louse  has  been  shown  to  be  the  trans- 
mitter of  relapsing  fever  in  India  also. 


RELAPSING  FEVER  —  TRANSMISSION 


45 


In  Europe  several  different  pests  are  probably  implicated  in 
the  transmission  of  relapsing  fever.  In  Persia  and  neighboring 
countries  the  miana  tick,  Argas  persicus  (see  p.  364,  and  Fig.  159), 
is  probably  the  chief  offender,  while  in  Russia,  Serbia  and  the 


Fig.  7.  Life  cycle  of  Spirochceta  gallinarum,  applicable  also  to  Sp.  dutloni  of 
relapsing  fever.  A,  multiplication  by  transverse  division  in  vertebrate  blood;  B, 
formation  of  coccoid  bodies  in  vertebrate  blood:  C,  infection  of  cells  of  tick  and 
formation  of  coccoid  bodies;  D,  multiplication  of  coccoid  bodies  in  tick;  E,  de- 
velopment of  spirochaete  forms  from  coccoid  bodies  after  reentering  vertebrate 
blood.      X  1500.     (After  Hindle.) 

Balkan  States  lice  and  probably  also  bedbugs  are  the  trans- 
mitters (see  p.  378).  It  is  noteworthy  that  relapsing  fever  al- 
ways thrives  best  in  those  countries  where  body  cleanliness  is 
neglected,  and  where  vermin  are  in  consequence  abundant.  In 
fact,  the  prevalence  of  relapsing  fever  in  any  country,  as  of  typhus, 


46  SPIROCHETES 

is  in  inverse  proportion  to  the  prevalence  of  the  use  of  soap  and 
water.  Relapsing  fever,  in  countries  where  it  is  transmitted  by 
lice,  always  spreads  most  rapidly  in  cold  weather  when  people 
are  huddled  together  in  stuffy,  filthy  houses,  thus  giving  the  lice 
ideal  opportunities  for  doing  their  evil  work. 

In  Mexico  and  Central  America  it  is  believed  that  certain  ticks, 
Ornithodorus  talaje  and  0.  turicata,  which  in  form  and  habits 
closely  resemble  the  African  relapsing  fever  tick,  transmit  the 
disease,  but  this  has  not  been  proved.  0.  turicata  is  said  to  be 
the  transmitter  in  Colombia,  but  the  bedbug  and  other  ticks  are 
also  suspected. 

Relapsing  fever  is  not  a  contagious  disease  as  was  formerly 
supposed.  A  typical  case  in  the  Bellevue  Hospital  in  New  York 
failed  to  spread  the  infection  to  anyone  else  during  the  89  days' 
stay  of  the  patient,  although  no  special  precautions  were  taken 
to  prevent  it  from  spreading. 

The  Disease.  —  In  the  human  body  the  spirochsetes  appear  to 
live  exclusively  in  the  blood,  where  they  become  fairly  common, 
though  never  abundant,  at  regular  intervals.  In  the  meantime 
they  apparently  disappear  though  they  are  undoubtedly  present 
either  in  the  granular  form,  or  else  in  such  limited  numbers  as 
to  be  practically  impossible  to  find.  The  repeated  increase  and 
decrease  of  the  spirochsetes  in  the  blood  goes  hand  in  hand  with  a 
recurring  fever  broken  by  periods  of  apparently  almost  normal 
health.  The  time  of  incubation  of  the  disease  varies  from  two 
days  to  two  weeks,  but  in  most  cases  the  initial  attack  comes  on 
the  third  or  fourth  day.  It  usually  begins  with  severe  chilly 
sensations,  headache  and  shooting  pains  in  the  limbs.  The 
ensuing  fever  lasts  intermittently  for  several  days,  being  accom- 
panied by  such  symptoms  as  rapid  pulse,  enlarged  spleen,  con- 
stipation, nausea  and  mental  disturbances.  After  several  days 
the  temperature  suddenly  drops  below  normal  and  remains  so 
for  a  period  of  seven  or  eight  days,  during  which  time  the  patient 
recovers  rapidly,  feels  perfectly  well  and  thinks  it  unnecessary  to 
remain  at  home  or  in  the  hospital  any  longer.  Then  comes  the 
first  relapse,  repeating  all  the  symptoms  of  the  first  attack,  some- 
times in  somewhat  milder  form.  Following  this  there  is  a  second 
period  of  apparently  normal  health,  usually  followed  by  a  second 
relapse,  this  time  much  milder.  The  number  of  relapses  varies: 
in  the  European  and  allied  types  the  second  relapse  is  mild,  and 


RELAPSING  FEVER  — TREATMENT  47 

is  the  last  one  felt;  in  the  African  type,  on  the  other  hand,  there 
are  usually  four  or  five  relapses,  of  shorter  duration  and  more 
irregular  in  occurrence.  In  a  Gibraltar  case  Manson  observed 
eight  distinct  relapses,  but  this  is  very  unusual.  Hemorrhages 
under  the  skin  and  in  various  organs  of  the  body  often  occur, 
and  cases  have  occurred  recently  in  Hungary  in  which  the  men- 
inges (tissues  covering  the  brain  and  spinal  cord)  were  severely 
affected,  causing  various  nervous  disorders.  Spleen,  liver  and 
other  organs  are  frequently  affected. 

Even  the  African  type  of  the  disease  does  not  ordinarily  have 
a  high  mortality,  though  some  epidemics  are  more  serious  than 
others.  In  an  epidemic  in  Tonkin  in  1912,  48  per  cent  of  703 
cases  were  fatal.  In  India  the  fatality  is  often  high  on  account 
of  the  well-meant  but  pernicious  habit  of  depriving  fever-stricken 
people  of  food,  thus  often  increasing  the  exhaustion  caused  by 
the  disease.  Abortion  is  a  common  result  in  pregnant  women. 
A  single  attack  gives  permanent  immunity  to  any  one  particular 
type  of  the  disease  but  not  to  others. 

Treatment  and  Prevention.  —  Ehrlich's  famous  spirochete 
poison,  "  No.  606,"  or  salvarsan,  destroys  the  spirochsetes  of 
relapsing  fever  more  readily,  if  anything,  than  it  does  other 
species  of  spirochsetes,  since  the  parasites  live  in  the  blood  stream 
into  which  the  drug  is  directly  injected.  A  single  injection 
nearly  always  causes  the  disappearance  of  the  parasites  from  the 
blood  and  prompt  recovery  from  all  symptoms  of  the  disease. 
Preventive  and  curative  inoculations  of  the  serum  of  highly  im- 
mune animals  has  been  found  to  be  effective  in  rats  and  monkeys. 
The  power  of  the  immune  serum  can  be  so  increased  by  repeatedly 
inoculating  an  animal  that  very  small  injections  of  it  are  sufficient 
not  only  to  cut  short  the  course  of  the  disease  in  these  animals 
but  also  to  give  an  immunity  of  considerable  duration.  It  is 
probable  that  the  same  serum  would  immunize  human  beings 
as  well. 

Eradication  of  vermin  from  person  and  home  and  avoidance 
of  places  where  infected  parasites  might  be  acquired  are  the 
most  important  protective  measures  in  places  where  an  epidemic 
is  raging.  Methods  for  the  control  of  ticks  are  discussed  on  page 
369,  of  lice  on  page  400  and  of  bugs  on  page  383.  Since  the 
parasites  are  not  ordinarily  introduced  directly  into  the  blood 
by  the  beak  of  the  transmitter,  but  are  simply  voided  with  the 


48  SPIROCHETES 

excrement  in  the  vicinity  of  the  wound,  careful  disinfection,  with 
alcohol  or  carbolic  acid,  of  the  wound  before  the  removal  of  the 
parasite  is  a  good  means  of  prevention  if  the  suspected  trans- 
mitter be  caught  in  the  act  of  biting. 

S3rphilis 

History.  —  There  are  few  diseases  which  mean  more  to  the 
human  race  as  a  whole  than  syphilis,  due  in  part  to  its  almost 
universal  distribution,  and  in  part  to  its  insidious  and  deceiving 
course,  thereby  leading  to  untold  misery  and  disaster.  Rosenau 
says  "  civilization  and  syphilization  have  been  close  companions  "; 
the  one  has  followed  in  the  wake  of  the  other  like  the  gueril- 
las behind  an  army.  Unlike  most  diseases,  syphilis  is  one  of 
whose  origin  among  civilized  nations  we  have  strong  evidence. 
There  are  many  reasons  for  believing  that  syphilis  was  acquired 
by  the  members  of  Columbus'  crew  when  they  discovered  the 
island  of  Haiti,  and  that  it  was  carried  back  to  Spain  by  them  on 
their  return.  These  adventurers  promptly  joined  the  army  of 
Charles  VIII  of  France  in  its  invasion  of  Italy  in  1494.  Soon 
after  the  army  had  triumphantly  set  up  a  court  in  Naples  it 
became  weakened  through  the  ravages  of  a  terrible  venereal 
disease  of  unusual  intensity,  hitherto  apparently  unknown  in 
Europe.  The  following  year  the  army  retreated  almost  in  a 
rout  and  was  broken  up,  the  miscellaneous  troops  scattering  all 
over  Europe  to  their  respective  home  countries,  and  carrying  the 
new  disease  with  them.  In  the  next  four  years  the  disease  had 
spread  to  practically  every  country  in  Europe,  and  was  soon  car- 
ried by  the  Portuguese  to  Africa  and  the  Orient.  The  venereal 
nature  of  the  disease  was  fully  recognized,  and  its  foreign  origin 
was  well  known,  each  nation  trying  to  shift  the  responsibility  to 
another  by  name,  many  peoples  calling  it  the  ''  French  disease," 
others  the  "  Spanish  disease,"  etc.,  while  the  Spanish  alone  seemed 
aware  of  its  real  origin  in  America  and  called  it  '^  espanola  " 
which  then  meant  Haiti.  The  absence  of  any  reference  to  a 
disease  resembling  syphilis  in  the  historical  records  before  the 
discovery  of  America;  the  absence  of  any  bones  showing  evidence 
of  syphilitic  attack  in  the  abundant  pre-Columbian  remains  in 
Europe,  and  abundance  of  such  bones  in  American  remains, 
many  of  which  must  certainly  be  pre-Columbian;    the  positive 


SYPHILIS  —  RECENT  HISTORY  49 

evidence  of  Spanish  physicians  and  historians  at  the  time  of  the 
return  of  Columbus;  and  the  severity  of  the  great  epidemic 
in  the  latter  part  of  the  15th  century,  —  it  being  almost  in- 
variable for  an  infectious  disease,  when  first  introduced  among  a 
new  people,  to  rage  with  unwonted  severity;  all  these  facts 
point  strongly  to  the  American  origin  of  syphilis. 

Interesting  as  is  the  early  history  of  the  disease,  the  recent 
history  is  infinitely  more  so.  By  the  beginning  of  the  twentieth 
century  medical  men  had  come  to  the  end  of  their  rope  in  knowl- 
edge and  treatment  of  the  disease,  and  found  themselves  at  a 
standstill.  But  in  1902  the  disease  was  successfully  transmitted 
to  animals  where  it  could  be  conveniently  studied;  in  1905 
Schaudinn  discovered  the  spirochsete,  Spirochceta  {or  Treponema) 
pallida  (Fig.  5C),  which  is  believed  to  cause  the  disease.  In 
1906  Wassermann  demonstrated  the  possibility  of  detecting 
latent  syphilis  by  the  reaction  which  bears  his  name;  in  1910 
Ehrlich  made  the  epoch-making  discovery  of  his  famous  drug, 
''  No.  606,"  or  salvarsan,  a  deadly  poison  for  spirochsetes  of  all 
kinds,  and  a  cure  for  syphilis  in  nearly  all  stages;  in  1913  the 
direct  relation  of  syphilis  to  insanity,  paralysis  and  other  diseased 
conditions  of  the  central  nervous  system  was  demonstrated  by 
the  discovery  of  the  organisms  in  the  cerebrospinal  fluid,  and  in 
the  same  year  a  method  of  destroying  the  parasites  in  the  central 
nervous  system  was  discovered.  There  is  no  other  instance  in 
the  history  of  medical  science  where  such  wonderful  strides 
have  been  made  in  such  a  short  time  in  the  knowledge  and  control 
of  a  disease.  At  the  beginning  of  the  twentieth  century  syphilis 
was  one  of  the  most  horrible,  hopeless  and  tragic  diseases  known 
to  ravage  the  human  body;  it  is  now  a  disease  which  can  be 
readily  recognized  even  in  latent  stages;  it  can  be  cured  in  its 
early  stages;  and  the  terrible  tragedies  resulting  from  apparent 
but  imperfect  cure  can  be  avoided.  Its  eradication,  however, 
will  not  soon,  if  ever,  be  accomplished,  since  in  this  are  involved 
some  of  the  most  intricate  moral  and  social  questions  with  which 
we  have  to  deal. 

Prevalence.  —  The  prevalence  of  syphilis  is  difficult  to  de- 
termine for  at  present  the  recording  of  syphilitic  cases  is  prac- 
ticed to  a  very  slight  extent,  and  accurate  data  can  be  obtained 
only  in  military  organizations  and  certain  public  and  private 
institutions.     Sir  William  Osier  places  syphilis  as  third  or  fourth 


50  SPIROCHETES 

of  the  killing  diseases.  The  use  of  the  Wassermann  reaction  for 
the  detection  of  syphilis  has  greatly  extended  the  possibility  of 
arriving  at  an  estimate  of  the  prevalence  of  the  disease,  and  has 
shown  that  it  is  far  more  common  than  was  formerly  believed. 
Yet  even  the  Wassermann  test  fails  in  about  10  per  cent  of  cases. 
It  is  now  known  that  the  disease  may  be  present  in  latent  but 
nevertheless  infective  form  for  many  years  after  all  active  symp- 
toms have  disappeared.  The  recently  published  report  of  the 
British  Royal  Commission  on  Venereal  Diseases  concluded  that 
the  number  of  people  infected  with  syphilis  cannot  fall  below 
ten  per  cent  in  large  cities,  and  that  at  least  one-half  the  regis- 
tered still-births  are  due  to  this  disease.  They  found  that  in 
Britain  this  as  well  as  other  venereal  diseases  is  most  prevalent 
in  the  unskilled  labor  class,  and  least  among  miners  and  agri- 
cultural laborers.  Fournier  estimated  that  in  Paris  15  per  cent 
were  infected.  In  China  syphilis  is,  next  to  tuberculosis,  the 
most  common  disease.  In  the  United  States  conditions  are 
no  better  than  elsewhere;  some  cities,  notably  San  Francisco, 
are  much  more  heavily  infected  than  others.  Of  111  cases  ad- 
mitted to  the  Children's  Hospital  in  Boston  31  per  cent  were 
infected  with  syphilis.  Of  102  children  admitted  to  a  Chicago 
hospital,  none  of  them  for  syphilis,  30  were  syphilitic.  In  the 
"  red  light  "  districts  of  cities,  which  undoubtedly  serve  as  the 
centers  of  distribution  for  the  disease,  the  per  cent  of  syphilitic 
prostitutes  is  very  high.  Dr.  Browning  found  every  one  of 
104  prostitutes  in  Glasgow  infected,  and  a  like  condition  among 
10,9  men,  women  and  children  classed  as  "  vagrants". 

According  to  Capt.  E.  B.  Vedder  of  the  U.  S.  Army,  the  sta- 
tistics compiled  from  over  1000  new  recruits  in  two  widely  sepa- 
rated camps  (in  New  York  and  Ohio  respectively)  showed  that 
over  19  per  cent  of  all  applicants  for  enlistment,  approximately 
one  in  five,  are  probably  syphilitic,  although  only  a  trifle  over  2 
per  cent  showed  any  symptoms  of  the  disease  which  would  ex- 
clude them  from  the  army  as  the  result  of  a  rigid  physical  exam- 
ination. From  this  Vedder  concludes  that  there  is  a  good  reason 
for  believing  the  percentage  of  syphilis  among  the  young  men  in 
civil  life,  between  the  ages  of  20  and  30,  to  be  fully  20  per  cent. 
"  It  means  that  when  a  man's  daughter  marries,  the  chances  are 
just  one  to  five  that  she  will  become  the  victim  of  '  damaged 
goods'."     Vedder  shows  further  that  in  the  relatively  select  class 


TRANSMISSION  OF  SYPHILIS  51 

of  young  men  at  West  Point  from  two  to  five  per  cent  are  prob- 
ably syphilitic.  In  the  U.  S.  Army,  as  a  whole,  Vedder  beheves 
an  estimate  of  16  per  cent  of  syphilis  among  the  whites  is  con- 
servative, and  his  statistics  show  that  the  per  cent  increases 
steadily  with  the  ages  of  the  enlisted  men,  and  as  the  years  of 
service  increase.  Among  enlisted  negroes,  who  are  notoriously 
more  syphilitic  in  civil  life  than  are  whites,  syphilis  is  two  or 
three  times  as  prevalent  as  among  white  enlisted  men.  "  This 
study  confirms  observations  that  have  already  been  published 
indicating  that  syphilis  is  so  prevalent  among  negroes  that  it  is 
possibly  the  greatest  single  factor  in  the  production  of  disability 
and  high  mortahty  rates  among  the  race."  The  figures  obtained 
from  an  examination  of  531  Porto  Rican  enlisted  men  are  most 
startling  of  all  —  over  50  per  cent  show  evidence  of  being  probably 
syphilitic. 

Transmission.  —  Syphilis  is  fundamentally  a  venereal  disease, 
transmitted  by  sexual  intercourse,  and  over  90  per  cent  of  cases 
are  undoubtedly  of  such  origin.  It  is  a  common  belief  that  this 
is  the  only  way  in  which  the  disease  can  be  acquired,  and  some- 
times an  unjust  stigma  of  shame  and  disgrace  is  attached  to  a 
perfectly  innocent  case  of  syphilis.  As  already  remarked,  in 
the  vast  majority  of  cases  the  parasites  are  directly  acquired 
from  their  usual  habitat  in  the  underworld,  but  over  20,000 
cases  of  innocent  syphilis  have  been  reported,  and  five  per  cent 
of  infections  occurring  in  the  army  are  of  innocent  origin.  A 
horrible  case  is  on  record  where  seven  young  women  at  a  church 
social  in  Philadelphia  acquired  syphilis  from  kissing  a  young 
man  who  had  a  syphilitic  sore  on  his  lip.  A  case  recently  oc- 
curred in  one  of  our  western  cities  which  was  ultimately  traced  to 
the  eating  of  apples  sold  by  an  Italian  who  was  in  the  habit  of 
spitting  on  his  fruits  and  rubbing  them  on  his  sleeve  to  shine  them. 
Public  drinking  cups,  public  towels  and  soiled  bed-linen  serve 
admirably  as  temporary  abodes  for  the  spirochaetes  of  syphilis, 
but  fortunately  these  curses  of  civilization  are  in  most  places 
abolished  by  law.  Unsanitary  barbers  and  dentists  can  easily 
spread  infection,  and  dentists  and  physicians  often  themselves 
contract  the  disease  from  handling  syphilitic  patients,  the 
spirochaetes  readily  entering  the  smallest  cut  or  abrasion  of  the 
skin.  Mid  wives  and  wet  nurses  are  likewise  exposed  to  infection 
from  diseased  babies,  as  are  the  babies  from  diseased  nurses. 


52 


SPIROCHETES 


Indeed,  when  we  think  of  the  many  ways  in  which  syphilis 
spirochsetes  may  be  transmitted  from  person  to  person  it  is  sur- 
prising that  the  number  of  innocent  cases  is  not  much  greater. 

The  Spirochaetes.  —  The  spirochsetes  of  syphiHs,  Spirochceta 
pallida  (Fig.  5C),  vary  in  length  from  four  to  14  fjL  (^Au  to  js\jf  of 
an  inch)  and  are  immeasurably  slender.  They  are  more  closely 
curled  than  the  spirochsetes  of  relapsing  fever,  having  usually 
from  six  to  14  very  regular,  short,  sharp  curls,  quite  different  from 
the  long  graceful  curves  of  a  relapsing  fever  parasite.  The 
living  organisms  are  very  active  and  dart  with  great  speed 
across  a  slide,  threading  their  way  between  blood  corpuscles  or 
cells.  The  spiral  turning  of  the  body  reminds  one  of  the  undulat- 
ing movements  of  a  swimming  snake.  Another  spirochsete,  Sp. 
refringens  (Fig.  5D),  is  often  found  associated  with  Sp.  pallida. 

During  the  early  stages 
of  their  sojourn  in  the  body 
the  spirochsetes  can  always 
be  found  in  the  primary  and 
secondary  lesions,  and  in  the 
neighboring  lymph  glands. 
During  the  second  phase 
of  the  disease  and  also 
toward  the  end  of  the 
first  phase  the  spirochaetes 
occur  in  variable  numbers 
in  the  blood,  and  very 
early  make  their  way  into 
the  cerebrospinal  fluid  in 
the  brain  and  spinal  cord. 
After  it  was  found  that 
the  spirochsetes  actually 
invade  the  central  nervous  system,  and  cause  diseases  of  it,  it  was 
supposed  that  this  occurred  only  occasionally  in  late  stages  of 
the  disease.  During  the  last  year  or  two  it  has  been  shown, 
however,  that  the  great  majority  (80  per  cent)  of  syphilitics  show 
distinct  pathological  changes  in  the  spinal  fluid,  due  to  spiro- 
chsetes in  it,  from  the  date  of  the  primary  sore,  and  are  therefore 
possible  candidates  for  syphilis  of  the  nervous  system.  During 
the  second  phase  the  spirochsetes  make  a  general  invasion  of 
the  entire  body,   later  showing  some  special  predilection  for 


Fig.  8.     Spirochceta  -pallida  in  liver  tissue 
of  a  congenital  syphilitic. 


COURSE  OF  SYPHILIS  53 

certain  tissues  or  organs.  The  gummy  sores  or  "  gummas  " 
which  often  break  out  during  the  third  stage  of  the  disease  have 
usually  been  considered  non-infective,  and  spirochsetes  could  not 
be  found  in  them.  Recently,  however,  the  parasites  have  been 
found  in  some  of  these  lesions,  also.  In  congenital  syphilis 
the  parasites  often  multiply  in  enormous  numbers  in  the  unborn 
child,  penetrating  practically  every  organ  and  tissue  of  the  body. 
The  liver  especially  is  often  found  literally  teeming  with  spiro- 
chsetes (Fig.  8). 

The  Disease.  —  SyphiHs  is  a  disease  which  has  no  equal  in  its 
deceptive  nature.  It  is  largely  due  to  this  fact  that  so  many 
tragedies  result  from  its  ravages.  Its  effects  on  the  individual 
are  often  horrible  enough,  leading  to  disease  of  almost  any  tissue 
or  organ  in  the  body,  but  it  is  only  when  judged  in  the  light  of 
the  additional  damage  that  is  done  to  the  innocent  wife  or 
husband,  as  the  case  may  be,  and  to  the  next  generation,  that 
the  true  meaning  of  syphilis  can  be  measured.  Syphihs  may 
remain  latent  and  unsuspected  for  twenty  years  or  more,  and  the 
carrier  still  be  infective.  Meanwhile,  perhaps  in  ignorance  of 
his  condition,  he  may  infect  a  hitherto  sound  person  whom  he 
has  taken  for  a  life  companion,  and  cause  her,  or  him,  to  be 
ravaged  and  slowly  destroyed  by  this  horrible  disease.  Worse 
than  this  his  chances  of  having  healthy  children  are  small.  It 
has  been  shown  that  about  45  per  cent  of  those  who  later  become 
victims  of  general  paralysis  from  syphilis  never  can  have  any 
children,  either  on  account  of  sterility  or  of  repeated  abortions. 
The  author  of  the  statement  in  the  Bible  that  "  the  sins  of  the 
fathers  shall  be  visited  upon  the  heads  of  the  children  unto 
the  third  and  fourth  generations  "  may  well  have  had  in  mind 
the  hereditary  effects  of  venereal  diseases,  but  he  might  have 
stated  further  that  often  there  is  no  third  or  fourth  generation. 
The  only  pity  of  it  is  that  this  is  not  always  the  case,  for  those 
who  are  brought  into  the  world  are  in  the  majority  of  cases 
hopelessly  handicapped  either  mentally  or  physically.  Feeble- 
mindedness is  five  times  as  common  in  syphilitic  families  as  in 
normal  ones.  There  is  some  reason  for  believing  that  the  hideous 
mentally  deficient  children  known  as  mongols  are  the  result  of 
syphilis  in  parents.  And  finally,  as  if  all  this  were  not  enough, 
the  carrier  of  latent  syphilis  may  later  develop  general  paralysis, 
or  some  other  disease  of  the  nervous  system  or  other  organs,  which 


64  SPIROCHETES 

will  render  him  an  ineffectual  social  unit,  and  make  him  and  his 
family  a  burden  to  the  community. 

In  the  majority  of  cases  the  disease  begins  with  a  hard  sore 
on  the  skin  or  mucous  membrane  known  as  the  ''  primary 
chancre."  This  usually  appears  at  the  point  of  infection  in  from 
ten  days  to  three  weeks  after  the  infection  occurs.  In  some  cases 
such  a  chancre  never  develops.  The  chancre  gradually  heals 
up  and  the  second  stage  begins,  in  which  general  constitutional 
symptoms  appear,  as  fever,  anemia  and  a  general  run-down 
condition  during  which  the  patient  is  very  susceptible  to  other 
diseases,  such  as  tuberculosis.  Often  there  is  an  extensive 
breaking  out  on  the  body,  production  of  scaly  patches  of  skin, 
and  inflammation  of  the  mucous  membranes  of  the  mouth  and 
throat. 

From  this  point  on  the  course  of  the  disease  depends  on  what 
particular  tissues  or  organs  the  spirochsetes  especially  attack, 
for  although  the  parasites,  as  said  before,  may  produce  disease 
almost  anywhere  in  the  body,  in  any  given  case  there  is  usually  a 
localization.  It  seems  that  certain  strains  of  the  parasites  have 
special  preference  for  certain  tissues.  The  differences  in  this 
respect  have  been  shown  by  Nichols  to  hold  good  through  many 
transfers  from  animal  to  animal,  and  visible  differences  in  the 
parasites  can  be  observed.  In  about  40  per  cent  of  cases  syphilis 
settles  in  the  nervous  system,  causing  a  great  variety  of  evil 
effects,  such  as  feeble-mindedness,  tabes,  or  locomotor  ataxia, 
general  paralysis,  epilepsy,  insanity  and  moral  defectiveness. 
Often  it  settles  in  the  skin  and  mucous  membranes,  producing 
the  gummy  sores  or  "  gummas  "  which  were  formerly  supposed  to 
be  the  usual  tertiary  stage  of  syphilis.  It  may  select  the  bones, 
muscles,  arteries,  heart,  reproductive  system,  or  any  other  part 
of  the  body,  in  each  case  producing  a  different  set  of  symptoms, 
but  in  every  case  weakening  the  vitality  and  leading  ultimately 
to  an  early  grave. 

An  active  attack  on  one  tissue  or  organ  of  the  body  seems  to 
have  an  inhibiting  effect  on  other  attacks.  It  is  well  known  that 
an  infected  person  presumably  with  an  active  attack  of  the 
spirochsetes  on  some  organ  in  his  body  will  not  develop  new 
lesions  when  re-infected.  Possibly  this  explains  why  there  is 
often  a  relapse  of  the  nervous  system  after  incomplete  treatment 
of  skin  syphilis.     The  spirochsetes  in  the  nervous  system  which 


DIAGNOSIS  OF  SYPHILIS  65 

are  not  reached  by  the  drugs  may  flare  up  and  produce  a  serious 
attack  after  the  spirochaetes  in  other  parts  of  the  body  have 
been  killed  and  the  skin  lesions  healed.  On  the  other  hand 
paralytics  with  an  active  attack  on  the  central  nervous  system 
seldom  show  any  other  symptoms.  Unborn  babies  seem  not 
to  be  subject  to  such  speciahzed  attacks,  but,  as  already  pointed 
out,  are  often  found  with  every  organ  and  tissue  in  the  body  full 
of  spirochaetes.  There  is  a  form  of  the  disease  occurring  in 
adults  known  as  "  malignant  syphilis  "  in  which  ulcerating  sores 
appear  early  and  gradually  eat  away  large  portions  of  the  skin. 
It  is  marked  by  extreme  anemia  and  great  weakness,  and  usually 
causes  an  early  death. 

Diagnosis.  —  The  modern  methods  of  diagnosing  syphilitic 
infection  have  revolutionized  our  knowledge  of  the  disease,  and 
have  done  much  toward  placing  its  treatment  and  control  on  a 
scientific  basis.  In  at  least  50  per  cent  of  syphilitic  cases  there 
are  no  symptoms  which  can  be  attributed  positively  to  syphilis, 
but  we  now  have  several  tests  for  the  disease,  two  of  which  are 
of  wide  application,  and,  together  with  the  characteristic  lesions 
in  certain  stages  of  the  disease,  make  it  possible  to  detect  syphi- 
lis in  practically  any  phase. 

The  simplest  of  these  indicators  for  syphilis  is  the  "  luetin 
test."  This  consists  of  the  injection  into  the  skin  of  a  sterile 
emulsion  of  the  dead  bodies  of  the  spirochaetes  from  a  culture. 
If  the  test  is  positive,  i.e.,  if  syphilis  is  present,  the  inoculation 
results  in  a  solid  or  a  pus-filled  pimple,  usually  appearing  in  a 
few  hours  but  sometimes  not  for  several  days.  This  test  is  ap- 
plicable to  latent,  tertiary  and  congenital  syphilis  and  does  not 
give  positive  results  during  the  active  primary  and  secondary 
stages  of  the  disease.  Its  value  lies  in  the  fact  that  it  is  sometimes 
sensitive  to  latent  infections  which  the  Wassermann  reaction, 
now  to  be  described,  does  not  demonstrate. 

The  Wassermann  reaction,  although  it  fails  to  reveal  syphilis 
in  rare  cases,  is  one  of  the  most  valuable  and  dependable  means 
of  diagnosis  known  in  medicine.  It  is  now  almost  universally 
used  in  well-equipped  laboratories.  The  reaction  is  also  positive 
to  some  other  diseases,  such  as  yaws  (also  a  spirochaete  disease), 
leprosy,  malaria,  scarlet  fever  and  other  diseases,  but  all  of 
these  can  be  diagnosed  beyond  doubt  by  other  means  and  thus 
prevent  a  false  diagnosis  of  syphilis.     The  reaction  in  brief  is  as 


56  SPIROCHETES 

follows:  A  little  serum  from  the  suspected  person  is  mixed  with 
an  extract  of  liver  or  heart  and  some  guinea  pig  serum  and  in- 
cubated a  short  time.  A  suspension  of  blood  corpuscles  and  a 
hemolytic  serum  is  then  added  and  the  mix- 
ture is  incubated  again.  If  the  suspected  serum 
is  not  syphilitic  the  blood  corpuscles  are  dis- 
solved by  this  mixture  and  the  serum  becomes 
*%•  B  i  ?o&  ^^^'  whereas  if  the  serum  is  syphilitic  no  change 
in  the  blood  corpuscles  takes  place,  and  they 
sink  to  the  bottom.  The  more  highly  syphi- 
FiG.  9.  WassTrmann  ^^^^^  ^^^  individual  the  more  complete  is  the 
Reaction.  Neg.,  nega-  sedimentation   of   the   corpuscles.     As   stated 

tive;  Pos.,  positive.        i     i?          iv  -r  i  i?  •     xi  • 

before  there  are  possible  sources  of  error  in  this 
test,  but  if  properly  made  with  standard  reagents,  and  with  suffi- 
cient control  tests,  it  can  be  confidently  relied  upon. 

Treatment.  —  There  are  many  quack  doctors  who  are  still 
practicing  the  same  inefficient  methods  of  curing  syphilis  that  were 
in  vogue  several  centuries  ago.  Syphilitic  sores  are  powdered 
and  cauterized  and  cured,  and  the  patient  is  given  to  believe 
that  his  disease  is  cured.  Unfortunately,  as  we  have  seen,  the 
course  of  the  disease  is  of  such  a  nature  that  the  doctor's  claim  of 
having  cured  may  be  borne  out  for  months  or  years  before  the 
insidious  disease  appears  again,  this  time  in  a  much  more  de- 
structive and  perhaps  incurable  state.  Superficial  treatment  of 
syphilis  sores,  accompanied  perhaps  by  a  few  "  tonic  "  pills,  in 
no  way  destroys  the  virulence  of  the  parasites  or  alters  the  future 
course  of  the  disease.  It  merely  makes  the  chance  of  correctly 
diagnosing  the  disease  more  difficult,  and  it  frequently  results  in  an 
unsuspecting  victim  carrying  the  disease  untreated  to  a  stage 
where  it  has  wrought  irreparable  damage  to  himself,  his  life-mate 
and  his  children. 

Treatment  of  the  disease  formerly  consisted  in  the  adminis- 
tration of  mercuric  chloride.  While  this  sometimes  effected  an 
apparently  complete  cure,  over  80  per  cent  of  syphilitics  suffered 
relapses  in  spite  of  the  most  persistent  treatment.  In  1910 
Ehrlich,  after  years  of  experimentation,  offered  humanity  his 
famous  preparation,  "  No.  606,"  known  as  salvarsan,  an  arsenic 
compound  which  is  deadly  to  spirochsetes.  When  this  drug  is 
injected  into  the  veins  of  a  syphilitic,  it  almost  immediately 
kills  all  the  spirochsetes  except  a  few  which  have  stowed  away  in 


SWIFT-ELLIS  TREATMENT  57 

inaccessible  parts  of  the  body,  and  these  must  be  caught  by  con- 
tinued administration  of  the  drug,  or  by  special  methods.  The 
most  successful  method  of  treatment  is  an  alternate  use  of 
mercury  and  salvarsan,  this  apparently  being  more  effective 
than  salvarsan  alone.  There  is  now  on  the  market  a  modified 
form  of  salvarsan,  known  as  neosalvarsan,  which  is  milder  in 
its  effects  on  the  body  but  usually  considered  less  powerful  in 
destroying  the  spirochetes.  Several  other  more  or  less  valuable 
substitutes  for  salvarsan  are  now  prepared.  On  account  of  the 
war,  salvarsan  itself,  a  German  product,  is  at  present  difficult  to 
obtain. 

Salvarsan  injected  into  the  veins  does  not  reach  the  spiro- 
chsetes  in  the  central  nervous  system,  and  since  it  is  too  injurious 
to  be  injected  directly  into  the  spinal  fluid,  the  usual  treatment 
of  syphilis  is  inapplicable  to  syphilitic  infections  of  the  nervous 
system.  An  injection  of  salvarsan  into  the  lymph  spaces  under 
the  fibrous  coverings  of  the  brain  is  sometimes  used,  but  is  not 
always  successful.  Swift  and  Ellis,  of  the  Rockefeller  Institute, 
discovered  in  1913  that  the  blood  serum  of  a  syphilitic  who  had  re- 
cently been  given  salvarsan  was  destructive  to  spirochsetes  and 
could  be  injected  into  the  spinal  fluid  without  injurious  results. 
Out  of  this  grew  the  so-called  Swift-Ellis  treatment  of  syphilis 
of  the  nervous  system  by  the  use  of  '*  auto-sal varsanized  serum," 
i.e.,  the  serum  of  the  patient  himself  after  having  been  given 
salvarsan  an  hour  before.  This  serum  is  heated  for  half  an  hour 
to  make  the  salvarsan  in  it  more  active,  then  diluted  and  injected 
into  the  spinal  canal.  While  complete  cures  in  late  cases  of 
paralysis  and  other  nervous  diseases  could  hardly  be  expected 
from  this  or  any  other  method,  the  results  which  have  been  ob- 
tained are  very  encouraging.  It  has  been  suggested  that  in  all 
cases  of  syphilis  the  Swift-Ellis  treatment  be  made  routine  as  a 
protective  measure  since,  in  the  majority  of  cases,  the  spiro- 
chaetes  invade  the  nervous  system  in  the  early  stages  of  the 
disease  and  the  consequences  of  their  establishment  there  are  so 
terrible  as  to  warrant  every  possible  preventive  measure. 

The  modern  methods  of  diagnosing  syphilitic  infection  have 
given  a  definite  standard  of  cure,  and  the  success  or  failure  of 
treatment  can  be  positively  demonstrated.  A  uniform  negative 
Wassermann  reaction  given  several  times  during  a  year,  and  ab- 
sence of  any  symptoms,  can  be  looked  upon  as  an  indication  of 


58  SPIROCHiETES 

cure,  though  some  doctors  consider  a  negative  Wassermann  reac- 
tion for  two  years  necessary  to  indicate  a  certain  cure  on  account 
of  rare  cases  of  relapse,  even  after  a  year  of  apparent  absence  of 
the  spirochaetes.  In  contrast  to  the  85  per  cent  of  relapses  which 
occurred  when  mercury  alone  was  used  to  treat  syphilis,  less  than 
four  per  cent  of  relapses  occur  after  treatment  with  both  mercury 
and  salvarsan.  Certainly  salvarsan  may  justifiably  be  con- 
sidered "  one  of  the  mightiest  weapons  in  medicine." 

Prevention.  —  The  control  and  ultimate  eradication  of  syphilis 
is,  in  spite  of  our  present  methods  of  diagnosis  and  treatment,  a 
dream  of  the  distant  future.  In  its  prevention  are  involved  so 
many  social  and  moral  problems  upon  which  people  will  not 
agree  that  the  task  is  beset  with  great  difficulties. 

According  to  Dr.  Snow  of  the  American  Social  Hygiene  Asso- 
ciation, the  means  of  controlling  and  preventing  syphilis  fall 
into  three  groups:  (1)  care  and  treatment  of  existing  cases  with 
a  view  to  preventing  their  spreading  the  infection,  (2)  protection 
of  the  uninfected  by  education  and  administrative  measures,  (3) 
the  development  of  social  defenses  against  the  disease. 

As  regards  the  first  type  of  preventive  measures,  practically 
all  medical  men  and  public  health  workers  are  agreed.  Adequate 
means  for  the  diagnosis  and  treatment  of  syphilis  should  be  pro- 
vided in  all  cases.  At  present  not  only  are  there  no  laboratories 
for  diagnosis  or  free  hospitals  or  clinics  for  treatment  provided  at 
public  expense,  but  most  of  our  private  physicians  and  hospitals 
shun  syphilitics,  and  refuse  to  care  for  them.  Many  physicians 
at  the  present  time  have  little  knowledge  of  venereal  diseases. 
The  suggestion  of  the  British  Royal  Commission  on  Venereal 
Diseases  urging  that  this  subject  be  given  a  prominent  place  in 
all  medical  schools  is  certainly  worthy  of  being  put  into  practice 
immediately.  In  many  of  our  large  cities  and  in  most  of  the 
small  ones  there  is  not  a  single  hospital  which  will  admit  a  patient 
for  a  venereal  disease.  Of  30  general  hospitals  in  New  York 
City,  only  ten  receive  patients  with  recognized  syphilis  in  the 
infective  stages.  Theoretically  a  syphilitic  in  the  infective  stages 
should  be  as  carefully  watched  and  cared  for  as  a  leper  or  small- 
pox patient,  yet  the  syphilitic,  the  victim  of  immorality  usually, 
but  sometimes  only  of  the  carelessness  of  some  other  culprit, 
is  turned  loose  without  treatment,  but  with  full  power  to  infect 
all  with  whom  he  comes  in  contact  directly  or  indirectly.     We 


PREVENTION  OF  SYPHILIS  59 

seem  to  have  made  little  advance  since  1496,  when  the  Parlia- 
ment of  Paris  decreed  that  all  persons  found  infected  with  syphilis 
should  leave  the  city  within  24  hours. 

The  British  Royal  Commission  urged  the  provision  of  ample 
facilities  for  free  diagnosis  of  these  diseases  and  for  free  treat- 
ment when  necessary.     Such  measures  have  already  been  at- 
tempted in  a  few  instances  in  our  own  country  and  their  ultimate 
success  on  a  large  scale  is  insured.     The  New  York  City  Health 
Department  in  a  single  year  examined  59,614  specimens  of  serum 
for  the  presence  of  syphilis  and  three-fourths  of  these  were  re- 
ceived from  private  physicians.     A  few  public  health  institutions 
are  doing  splendid  work  in  the  operation  of  a  department  for  the 
diagnosis  of  venereal  diseases  and  the  giving  of  personal  advice. 
The  Oregon  State  Board  of  Health  is  undertaking  an  extensive 
correspondence  with  persons  in  all  parts  of  the  state  who  write 
for  information  in  response  to  venereal  disease  placards  posted  in 
appropriate  places.     The  provision  of  ample  facilities  for  the 
free  treatment  of  syphilis  in  the  way  of  hospital  service  when 
necessary,  of  proper  medication,  and  of  the  extension  of  Social 
Service  hospital  work  is  something  which  we  have  only  begun  to 
touch  upon,  but  which  will  undoubtedly  come  in  time.     The 
fact  that  no  facilities  have  hitherto  been  provided  for  the  care 
of  syphilitics  either  at  public  expense,  or  in  the  private  practice 
of  physicians  and  hospitals,  is  a  disgrace  to  our  civilization  and  a 
menace  to  our  health.     The  medical  prevention  of  syphilitic  in- 
fection after  exposure  to  it  is  possible  and  succeeds  in  the  great 
majority  of  instances  if  attended  to  within  a  few  hours  after  ex- 
posure.    The  use  of  self-applied  medical  treatments  has  been 
fairly  successful  in  military  life,  but  as  shown  by  Dr.  Snow  it  is 
of  doubtful  value  in  civil  life,  since  the  intelligence  required  to 
apply  medical  preparations  properly  is  lacking  in  those  who  need 
it  most  —  immature  boys,  drink-befuddled  men,  defective  girls, 
and  the  average  prostitutes.     These  classes  constitute  the  bulk 
of  the  citizens  who  become  exposed  to  infection  and  since  the 
personal  supervision  of  a  physician  is  necessary  in  most  cases, 
it  might  best  be  required  in  all.     Private  physicians,  dispensary 
officers  and  the  health  department  staff  are  the  persons  qualified 
to  employ  medical  treatment  designed  to  prevent  infection  after 
exposure  to  it.     Avoidance  of  exposure  constitutes  the  best  and 
only  safe  preventive  measure  before  exposure. 


60  SPIROCHETES 

As  to  the  second  type  of  prevention,  the  protection  of  the  unin- 
fected by  education  and  administrative  measures,  great  advances 
are  being  made.  One  of  the  most  important  measures,  and  one 
to  which  we  are  slowly  coming,  is  the  compulsory  notification  of 
the  Public  Health  Department  of  all  cases  of  venereal  diseases  so 
that  whatever  action  seems  best  may  be  taken  to  safeguard  the 
public  health.  There  can  be  no  question  but  that  such  a  record- 
ing of  venereal  diseases  would  work  for  the  best  good  of  all  con- 
cerned, both  the  patient  and  the  public.  Laws  compelling  the 
notification  of  health  departments  of  venereal  diseases  now  exist 
in  eleven  states  and  a  number  of  cities  in  the  United  States, 
but  only  in  rare  instances  are  they  enforced.  Such  a  law  in 
modified  form  has  been  passed  and  is  being  enforced  in  Western 
Australia. 

With  the  notification  of  venereal  diseases,  many  other  prac- 
tical measures  could  be  inaugurated,  such  as  the  exclusion  of 
infectious  syphilitics  from  occupations  connected  with  the 
preparation  and  serving  of  food;  the  careful  instruction  of 
syphilitics  concerning  various  phases  of  their  disease,  and  possible 
means  of  transmission,  thus  in  many  cases  securing  their  active 
cooperation;  and  the  effective  prevention  of  the  marriage  of 
syphilitics.  The  last  is  one  of  the  most  important  measures 
that  could  be  adopted.  Many  states  at  present  prohibit  the  mar- 
riage of  persons  with  venereal  diseases  but  without  enforcement 
of  notification  these  laws  are  worse  than  useless,  since  they  may 
give  a  false  sense  of  security.  Knowing  the  awful  consequences 
of  inherited  syphilis  it  is  the  duty  of  society  to  prevent  the 
marriage  of  syphilitics  even  with  the  full  knowledge  and  consent 
of  both  parties.  The  Royal  Commission  urged  only  the  full 
information  of  the  undiseased  party  in  marriage,  allowing  the 
union  to  be  made  if  then  consented  to.  In  this  they  seem  not 
to  have  given  due  consideration  to  the  rights  of  the  next  genera- 
tion. With  compulsory  notification  of  venereal  diseases,  and  a 
law  refusing  a  marriage  license  to  any  person  who  has  or  has  had 
syphilis  and  cannot  pass  the  accepted  laboratory  tests  for  the 
disease,  the  pitiful  results  of  hereditary  syphilis  could  be  largely 
prevented.  Even  the  remote  possibility  of  the  spectacle  of  a 
diseased  wife  and  of  stillborn,  insane,  or  physically  imperfect 
children  should  be  enough  to  induce  any  man  worthy  of  the 
name  to  take  every  precaution  to  avoid  such  a  tragedy,  but  if 


SYPHILIS  AND  PROSTITUTION  61 

he  is  unwilling  to  do  this  for  himself  and  his  posterity,  social  laws 
should  do  it  for  him. 

Sanitary  laws  are  in  effect  in  many  places  which  help  to  pre- 
vent infection  from  such  sources  as  public  drinking  cups,  towels, 
bed-linen,  and  other  articles,  but  such  laws,  excellent  as  far  as  they 
go,  are  inadequate,  since  no  law  can  cover  all  the  articles  which 
may  be  rendered  infective  by  contact  with  a  syphilis  sore.  One 
common  source  of  infection,  though  more  for  gonorrhea  than  for 
syphilis,  is  the  improperly  constructed  toilets  in  public  schools. 
These  are  usually  built  so  high,  and  of  such  a  type  that  school 
children,  little  girls  especially,  are  exposed  to  infection  every 
time  they  use  them.  Many  cases  of  venereal  diseases  in  school 
children,  particularly  in  larger  cities,  have  been  traced  to  this 
source. 

No  preventive  measure  which  does  not  strike  directly  at  the 
primary  source  of  infection  can  be  adequate  in  coping  with  any 
disease.  Just  as  we  fight  malaria  through  the  mosquito,  sleep- 
ing sickness  through  tsetse  flies  and  typhoid  through  contami- 
nated water  and  houseflies,  so  we  must  fight  syphilis  and  other 
venereal  diseases  through  prostitution.  The  abolishment  of  this 
vice  would  unquestionably  mean  the  abolishment  of  venereal 
diseases.  At  present,  at  least  in  many  places,  this  is  certainly 
not  possible.  The  abolition  of  "  red  Hght  "  districts  is  invariably 
followed  by  a  parallel  increase  in  clandestine  prostitution,  luring 
many  who  would  abstain  from  unmasked  brothels,  to  say  nothing 
of  the  increase  in  seduction  and  rape  of  innocent  girls.  The 
most  feasible  plan  at  present,  as  successfully  tried  in  many 
European  cities,  especially  Germany,  is  the  municipal  supervision 
of  restricted  "  red  light "  districts.  By  continuous  medical 
attendance,  and  the  enforcement  of  strict  sanitary  measures,  the 
normal  spread  of  disease  from  this  source  has  been  reduced  to  a 
great  extent.  It  may  be  argued  that  municipal  control  of  prosti- 
tution implies  public  sanction  of  it,  and  is  therefore  morally 
wrong.  This  perhaps  is  true  but  there  can  be  no  question  about 
the  futility  of  attempting,  at  the  present  state  of  our  civilization, 
to  abolish  prostitution  or  even  to  lessen  it  materially  by  passing 
laws  against  it.  In  view  of  this  it  is  merely  a  question  of  a  greater 
or  lesser  evil,  and  there  can  be  no  moral  crime  in  lessening  the 
dangers  from  an  evil  which  we  are  powerless  to  destroy.  It  may 
be  said  that  the  lessening  of  danger  from  disease  in  houses  of 


62  SPIROCHiETES 

prostitution  will  increase  their  popularity.  The  same  argument 
might  be  used,  and  has  been  used  by  the  ultramoralists,  to  show 
that  it  is  morally  wrong  to  attempt  to  cure  venereal  diseases, 
since  this  lessens  the  terror  of  them.  Such  arguments  might  have 
more  force  if  syphilis  were  a  disease  which  affects  only  the  indi- 
vidual, and  was  not  a  source  of  danger  and  burden  to  the  com- 
munity. Moreover  it  seems  doubtful  whether  the  person  whose 
character  is  such  a  combination  of  moral  weakness  and  cowardice 
that  he  shuns  houses  of  prostitution  only  from  dread  of  disease, 
will  not  spend  his  time  in  seducing  innocent  girls,  or  in  other 
hardly  less  despicable  crimes.  It  may  further  be  pointed  out 
that  disease  and  immorality  go  hand  in  hand.  A  healthy  body 
is  conducive  to  a  healthy  mind,  so  by  eliminating  disease  we 
would  be  doing  at  least  as  much  toward  giving  a  death  stab  to 
immorality  as  toward  extending  it. 

The  medical  supervision  of  prostitution,  adopted  as  a  tempo- 
rary measure,  should  be  accompanied  by  efforts  toward  its 
ultimate  reduction.  The  abolition  of  alcoholic  drinks,  the  im- 
provement of  conditions  in  slums,  the  furnishing  of  decent 
surroundings  and  wholesome  sports  and  exercises,  and  the  en- 
forcement of  minimum  wage  laws  for  women  are  all  measures 
which  tend  toward  the  reduction  of  prostitution,  but  foremost 
of  all  such  measures  should  be  education;  in  this  lies  our  most 
powerful  weapon  against  immorality  and  venereal  disease.  Hos- 
pitals, public  schools,  churches,  libraries  and  the  lecture  plat- 
form all  have  the  power  of  spreading  the  gospel  of  sex  hygiene, 
each  in  its  own  way,  each  in  a  way  especially  suited  to  its  listeners. 
Even  the  theatre  can  enter  the  field  of  education  and  it  has  done 
so.  The  play,  and  the  motion  picture  patterned  after  it,  entitled 
''  Damaged  Goods,"  in  the  estimation  of  the  author,  has  done  a 
great  deal  of  practical  good.  Yet  many  ministers,  teachers  and 
newspapers,  often  in  total  ignorance  of  the  real  nature  of  the 
play,  and  in  absolute  neglect  of  their  own  opportunities  for 
educating,  have  severely  criticized  the  play  as  "  immoral."  Such 
men  and  women,  who  should  know  better,  are  nothing  short  of 
a  disgrace  to  the  institutions  they  represent  and  are  largely 
responsible  for  the  present  popular  ignorance  concerning  one  of 
the  matters  of  most  vital  interest  to  humanity  —  sex  hygiene. 


SPIROCH^TA  PERTENUIS  63 


Yaws 


A  common  feature  of  nearly  all  tropical  countries  is  the  disease 
known  as  yaws  or  frambesia.  In  the  Fiji  Islands  all  healthy 
children  are  expected  to  pass  through  an  attack  of  yaws  and  are 
sometimes  inoculated  with  it  by  their  parents.  It  is  common  in 
many  parts  of  equatorial  Africa,  particularly  on  the  West  Coast. 
In  the  West  Indies  it  is  also  a  very  common  disease,  especially  in 
the  islands  which  are  largely  inhabited  by  negroes.  There  is 
some  evidence  that  yaws  was  imported  to  America  from  Africa 
with  the  slaves  as  were  some  others  of  the  most  troublesome  Amer- 
ican diseases.  In  Brazil  the  disease  is  called  "  buba  brasiliensis  " 
and  is  often  confused  with  Leishmanian  diseases. 

The  parasite  which  is  the  cause  of  this  loathsome  disease  is  a 
spirochete,  Sp.  pertenuis,  which  is  hardly  distinguishable  from 
the  spirochsete  of  syphilis,  and  was  for  a  long  time  thought  to  be 
identical  with  it.  Recent  investigations,  however,  have  shown 
that  there  are  some  slight  differences  in  the  two  parasites,  though 
not  enough  to  be  recognizable  by  anyone  but  an  expert.  Like 
the  spirochsete  of  syphilis,  Sp.  pertenuis  inhabits  many  different 
organs  and  tissues  of  the  body,  being  found  especially  in  the 
spleen  and  lymph  glands  and  in  the  tumor-like  "  yaws."  It  is 
not  yet  conclusively  proved  that  yaws  and  syphilis  are  not  slightly 
different  types  of  the  same  disease,  though  most  workers  believe 
in  their  distinctness,  and  for  practical  purposes,  at  least,  it  is  best 
to  consider  them  as  distinct.  One  of  the  arguments  in  favor  of 
the  unity  of  the  two  diseases  is  that  typical  syphilis  seldom  occurs 
where  yaws  is  prevalent,  and  vice  versa,  but  this  may  be  due  to 
a  reciprocal  immunity,  i.e.,  yaws  giving  immunity  to  syphilis,  and 
syphilis  to  yaws. 

The  Disease.  —  In  from  12  to  20  days  and  occasionally  longer 
after  infection  constitutional  symptoms  appear,  such  as  fever, 
rheumatic  pains,  and  general  illness.  These  symptoms  are  some- 
times very  severe,  but  usually  they  are  slight  and  often  hardly 
noticeable.  After  several  days  of  such  symptoms  there  appears  a 
peculiar  powdery  scaling-off  of  the  skin,  sometimes  almost  invisible 
but  at  other  times  making  white  marks,  especially  conspicuous 
on  the  dark  skin  of  negroes.  After  several  days  little  pimples 
appear  over  the  hair  follicles  in  the  patches  of  powdery  skin. 
As  these  grow  the  raw  flesh  from  beneath  pushes  the  horny 


64  SPIROCHiETES 

epidermis  up,  causing  it  to  crack  over  the  surface  in  such  a  way 
as  to  give  the  Httle  tumor  the  appearance  of  a  raspberry.  Little 
yellow  summits  soon  develop  on  the  tumors,  composed  not  of 
pus  but  of  a  cheesy  material.     Some  of  the  pimples  grow  no 

further,  but  most  of  them  become  capped 
over  with  the  yellow  cheesy  substance 
which  catches  and  holds  particles  of  dust, 
and  thus  become  very  dirty.  These  are 
the  "  yaws  "  from  which  the  disease  takes 
its  name.  During  their  formation  they 
cause  some  itching,  but  are  not  painful. 
They  reach  the  height  of  their  develop- 
ment in  12  or  14  days  and  then  usually 
begin  to  shrink,  the  dirty  yellow  cap,  now 
dark  colored,  falling  off  and  leaving  a 
sound  patch  of  pale  skin.  Sometimes, 
^''*  }?k  \T^^  ""^ ^^'^^'     however,  though  in  less  than  ten  per  cent 

(After  Manson.)  ,  .  .      , 

of  cases,  ulceration  of  the  yaws  takes 
place,  but  this  is  probably  due  to  comphcating  infections.  The 
time  that  the  disease  lasts  varies  greatly  according  to  the  general 
health  and  constitution  of  the  patient.  In  normal  mild  cases  it 
may  be  all  over  in  less  than  two  months,  while  in  weak  or  sickly 
individuals  crop  after  crop  of  yaws  may  appear  for  months  or 
years,  recurring  at  irregular  intervals.  There  is  some  evidence  also 
that  there  may  be  a  rare  tertiary  stage  of  yaws  corresponding  to 
a  similar  stage  in  syphilis,  characterized  by  a  diseased  condition 
of  the  bones  of  the  arms  and  legs,  ulcers,  etc.,  though  this  may 
often  be  due  to  mixed  infections  with  syphilis  or  other  diseases. 
The  disease  known  as  gangosa,  prevalent  in  Guam  and  other  East 
Indian  Islands,  is  thought  by  some  to  be  a  consequence  of  yaws. 
Yaws  is  very  seldom  a  fatal  disease  except  in  young  children. 
Like  syphilis  it  is  very  contagious,  but  the  parasites  are  not 
transmitted  from  mother  to  baby  before  birth  or  by  nursing. 

Treatment  and  Prevention.  —  Care  of  the  general  health  of 
yaws  patients  and  conditions  leading  to  the  free  eruption  of 
the  yaws  aid  much  in  shortening  and  alleviating  the  course  of 
the  disease.  Salvarsan  is  poisonous  for  the  parasites  of  yaws 
as  it  is  for  other  spirochsetes,  and  is  an  almost  sure  cure  at  any 
stage  of  the  disease  when  injected  either  into  the  veins  or  muscles. 
In  experimental  animals  the  parasites  disappear  within  24  hours 


INFECTIOUS  JAUNDICE  65 

after  the  injection  of  salvarsan.     Galyl  and  other  arsenical  sub- 
stitutes for  salvarsan  are  also  effective  against  the  disease. 

The  suppression  of  yaws  in  communities  where  it  is  common 
consists  largely  in  affording  isolated  hospitals  or  houses  for 
yaws  patients  and  in  preventing  the  patients  by  proper  care  and 
treatment  from  spreading  the  disease  by  contagion.  Personal 
care  on  the  part  of  the  patient  is  often  more  than  could  be 
expected,  considering  that  yaws  is  most  common  among  half- 
civilized  and  ignorant  tropical  races.  However,  the  lure  of  a 
comfortable  and  congenial  ward  where  he  could  get  good  treat- 
ment would  undoubtedly  induce  many  a  native  to  submit  to  the 
practice  of  being  sanitary,  however  it  might  grate  upon  his  nerves 
at  first.  His  accounts  of  the  good  treatment  received  would 
help  in  luring  others,  and  what  few  ideas  of  sanitation  he  might 
have  retained  would  help  in  spreading  the  gospel  of  sanitation. 
In  this  way  the  prevalence  of  the  disease,  at  least  in  local  areas, 
could  be  greatly  reduced,  and  public  money  used  for  such  pur- 
poses could  be  considered  well  spent. 


Infectious  Jaundice  or  Weil's  Disease 

In  parts  of  Europe  and  in  Japan,  and  also  reported  from  various 
parts  of  North  America,  there  occurs  a  disease  characterized 
especially  by  fever  and  jaundice  {i.e.,  affection  of  the  liver  causing 
a  marked  sallow  color  due  to  bile  pigments  in  the  blood) ,  the  cause 
of  which  has  long  been  a  puzzle  to  medical  men.  It  has  often 
been  confused  with  yellow  fever  and  with  bilious  typhoid,  and  it 
is  not  certain  even  now  that  the  latter  is  not  a  very  severe  type  of 
Weil's  disease.  Early  in  1915  the  connection  of  a  new  species 
of  spirochaete,  Leptospira  icterohcemorrhagice,  with  the  disease  was 
discovered  by  two  Japanese  investigators,  Inada  and  Ido.  Later 
in  the  same  year,  and  independent  of  the  Japanese  work,  the  same 
organism  was  discovered  in  Germany  in  ccJnnection  with  WeiPs 
Disease,  the  German  investigators  suggesting  the  name  Sp. 
nodosa.  One  could  almost  wish  that  the  German  name  had  been 
given  first! 

The  Disease.  —  A  week  or  more  after  infection  the  first  symp- 
toms appear  rather  suddenly  in  the  form  of  headache,  high 
fever,  and  a  feeling  of  leaden  fatigue  in  the  legs  which  soon 
changes  to  intense  pains.     The  muscles  become  so  tender  that 


66 


SPIROCH.ETES 


even  a  slight  touch  is  unbearable.  Usually  the  spirochsetes  are 
abundant  in  the  liver,  suprarenals,  blood  and  other  organs  and 
tissues  during  this  initial  'Afebrile"  stage  of  the  disease,  but  they 
are  destroyed  in  the  liver  and  suprarenals  by  antibodies  usually 
by  the  seventh  day.  During  the  second  week  of  the  disease, 
termed  the  ''icteric"  stage,  the  fever  subsides  and  marked  jaundice, 
accompanied  by  swelling  and  pain  in  the  liver,  usually  appears, 
though  this  symptom  is  sometimes  evident  as  early  as  the  third 
day.  In  some  cases,  in  Europe  at  least,  jaundice  may  not  appear 
at  all.  The  fever  usually  reappears  in  milder  form  about  the 
end  of  the  second  week,  but  it  is  of  short  duration.  Such  symp- 
toms as  vomiting,  nose  bleed,  upsetting  of  the  digestive  system, 
swollen  spleen,  weak  but  rapid  pulse,  and  meningitis  are  usually 
associated  with  the  disease,  and  kidney  trouble  is  nearly  always 
present,  and  is  'sometimes  more  severe  than  the  jaundice.     A 

tendency  for  the  mucous 
membranes  and  various 
organs  to  bleed  is  a  common 
and  dangerous  symptom. 
During  the  icteric  stage  of 
the  disease  the  spirochsetes 
disappear  from  the  blood, 
and  are  gradually  destroyed 
in  other  parts  of  the  body; 
they  persist  longest  in  the 
kidneys,  since  the  antibodies 
which  destroy  them  else- 
where are  apparently  ineffec- 
tual against  those  situated 
in  the  kidney  tubules.  They 
continue  to  be  excreted  with 
the  urine  for  six  or  seven 
weeks,  though  nearly  all  symptoms  usually  disappear  much  earlier. 
If  death  occurs,  it  nearly  always  comes  between  the  eighth  and 
sixteenth  days  of  illness.  The  disease  is  said  to  be  not  as  severe 
in  Europe  as  in  Japan,  the  mortality  among  infected  soldiers  in 
Flanders  being  less  than  six  per  cent. 

The  spirochaetes  are  found  in  the  blood,  the  cerebrospinal  fluid, 
and  in  many  of  the  tissues  of  the  body,  especially  the  liver  and  the 
kidneys.     They  vary  in  length  from  only  four  or  five  ii  to  20  fj. 


Fig.  11.  Liver  of  patient  who  died  from 
Weil's  disease  on  sixth  day,  showing  Spiro- 
chceta  icterohemorrhagice  in  tissue.  X  200. 
(Sketched  from  figure  by  Inada  et  al.) 


TRANSMISSION   OF  INFECTIOUS  JAUNDICE  67 

i^jyuTj  to  Y3fVn  of  an  inch)  and  are  characterized  by  pointed  and 
usually  hooked  ends  (Fig.  5G).  According  to  the  workers  in 
Japan  the  undulations  are  irregular  and  more  like  those  of  the 
relapsing  fever  spirochsetes  than  like  those  of  the  spirochsete  of 
syphilis.  Noguchi,  however,  states  that  the  number  of  coils  in 
a  given  length  is  greater  than  that  in  any  spirochsete  hitherto 
known,  there  being  ten  or  twelve  coils  in  five  n  (^Air  of  an  inch). 
The  figure  (Fig.  5G)  shows  only  the  gross  undulations  of  the 
organism  and  not  the  individual  coils.  From  their  descriptions 
it  would  seem  that  the  Japanese  workers  have  mistaken  these 
gross  undulations  for  the  true  coils.  Noguchi  believes  this 
spirochsete  to  have  characteristics  sufficiently  distinctive  to  war- 
rant its  being  placed  in  a  new  genus,  Leptospira.  The  spiro- 
chaetes  become  most  numerous  from  the  13th  to  the  15th  day  of 
illness,  and  begin  to  diminish  and  degenerate  by  the  24th  or 
25th  days,  though  they  may  continue  to  be  excreted  with  the 
urine  for  six  or  seven  weeks. 

It  is  probable  that  the  spirochsetes  gain  access  to  the  body 
either  by  way  of  the  alimentary  canal  or  directly  through  the 
skin.  The  disease  can  be  experimentally  transmitted  to  guinea- 
pigs  by  applying  an  emulsion  of  diseased  liver  to  the  shaved  but 
uninjured  skin,  infection  taking  place  in  as  short  a  time  as  five 
minutes.  Infection  is  more  certain  if  any  abrasion  of  the  skin 
exists. 

It  has  been  shown  that  both  the  urine  and  the  faeces  of  infected 
people  contain  living  spirochsetes  and  that  these  excretions  are 
infective.  Since  infection  can  occur  directly  through  the  skin 
contact  with  contaminated  ground  is  dangerous  and  probably 
accounts  for  the  prevalence  of  the  disease  in  certain  mines  in 
Japan.  Rats  have  been  shown  by  Japanese  investigators  to 
serve  as  a  reservoir  for  infectious  jaundice.  The  spirochsetes  are 
very  common  in  rats,  especially  in  the  kidneys,  being  con- 
stantly excreted  with  the  urine.  Examination  of  86  rats  in 
cities  and  coal  mines  in  Japan  where  infective  jaundice  occurs 
showed  that  nearly  40  per  cent  carried  virulent  spirochsetes  in  their 
kidneys,  in  most  cases  demonstrable  by  microscopic  examination 
of  kidney  tissue  or  urine  as  well  as  by  experimental  inoculations. 
In  America  the  parasites  have  been  demonstrated  in  wild  rats 
caught  in  the  vicinity  of  New  York  City  and  in  Nashville,  Tenn. 
The  ease  with  which  rats  may  contaminate  food  with  their  ex- 


68  SPlROCHiETES 

cretions  makes  it  appear  probable  that  these  animals  are  an  im- 
portant means  of  spreading  the  disease,  and  this  most  readily 
explains  the  common  occurrence  of  epidemics  in  families.  Two 
cases  have  been  reported  as  having  resulted  from  the  bites  of 
rats.  That  rats  serve  to  spread  Weil's  disease  in  Europe  also 
appears  evident  from  its  common  occurrence  where  rats  are 
abundant.  In  Europe  butchers  are  especially  prone  to  it,  and 
severe  epidemics  of  it  have  broken  out  in  the  rat-infested  war 
trenches. 

Treatment  and  Prevention.  —  The  Japanese  investigators  find 
evidence  that  salvarsan  is  destructive  to  Sp.  iderohemorrhagice, 
but  their  results  are  far  from  convincing  and  the  German  inves- 
tigators say  that  salvarsan  does  not  destroy  the  parasites.  More 
investigation  and  experimentation  needs  to  be  done  before  this 
question  can  be  settled. 

Investigators  of  both  countries  have  had  greater  success  in 
treating  the  disease  by  injection  of  the  serum  of  a  convalescent  or 
of  an  animal  which  has  become  immune.  The  Germans  found 
the  convalescent  serum  effectual,  either  as  a  preventive  or  for 
cure,  when  diluted  100  times.  Japanese  workers,  on  the  other 
hand,  put  far  more  faith  in  active  immunization.  They  inject 
spirochsetes  which  have  been  weakened  by  subjection  to  very 
dilute  carbolic  acid  and  left  on  ice  for  a  week.  Guinea-pigs  can 
be  immunized  by  such  injections,  or  even  by  injections  of  dead 
parasites  or  the  products  of  their  disintegration. 

Prevention  of  this  disease,  as  of  plague,  evidently  resolves  itself 
largely  into  rat  destruction  by  poisoning,  trapping  and  rat-proof- 
ing. Some  reduction  should  be  obtained  by  keeping  food  where 
rats  cannot  get  access  to  it,  and,  of  course,  where  it  cannot  be- 
come infected,  directly  or  indirectly,  by  the  excretions  of  human 
patients.  However,  since  the  parasites  are  able  to  penetrate 
directly  through  thin  skin,  especially  if  there  are  any  abrasions, 
care  should  be  taken  to  prevent  contamination  with  urine  of 
objects  or  surfaces  which  are  likely  to  come  in  contact  with  the 
hands  or  other  parts  of  the  body  of  other  people.  As  remarked 
before,  epidemics  in  mines  are  largely  due  to  insanitary  habits 
and  contamination  of  the  ground.  In  mines  or  other  places 
where  sanitary  conditions  are  difficult  to  enforce,  wholesale  im- 
munization would  probably  be  effective,  but  good  results  can 
also    be   obtained   by   disinfecting   the   ground.     According   to 


YELLOW  FEVER 


69 


Japanese  authors,  two  epidemics  in  coal  mines  have  already  been 
prevented  by  the  latter  method,  combined  with  removal  of  inun- 
dated water. 

Yellow  Fever 

Distribution.  —  Yellow  fever  is  a  disease  which  is  especially 
characteristic  of  the  seaport  towns  of  tropical  America,  although 
it  is  also  endemic  on  the  west  coast  of  Africa,  whence  many  think 
it  was  imported  to  America  with  the  slaves.  Its  approximate 
distribution  is  shown  in  Fig.  12.  In  the  past,  before  the  days 
of  the  strict  quarantine  laws  now  enforced,  serious  epidemics  of 
this  dread  disease  appeared  during  the  summer  in  numerous 
seaports  of  subtropical  and  temperate  countries.     At  one  time 


Fig.  12.     Map  showing  geographic  distribution  of  the  yellow  fever  mosquito, 
Aedes  calopus  (black  lines) ,  and  former  distribution  of  yellow  fever  (red  stipple) . 

there  was  no  city  on  the  whole  Atlantic  and  Gulf  coasts  of  the 
United  States  which  was  exempt  from  yellow  fever  epidemics,  and 
the  disease  exerted  a  serious  influence  on  the  economic  conditions, 
especially  of  our  Southern  States.  In  New  Orleans  there  have 
been  epidemics  which  have  cost  thousands  of  lives,  the  last  one 
occurring  in  1905.  In  temperate  cities  the  epidemics  always 
ended  with  the  coming  of  frost  and  destruction  of  the  transmitting 
mosquitoes.  Now  the  situation  is  quite  different  and  there  is 
no  reason  to  believe  that  the  world  will  ever  again  see  such  a  sight 


70  SPIROCHETES 

as  was  formerly  only  too  common  —  a  frantic,  terrorized  city 
helpless  in  the  grip  of  a  deadly  yellow  fever  epidemic.  No  epi- 
demic has  occurred  in  the  United  States  since  1905  and  many 
of  the  tropical  cities,  such  as  Havana,  Manaos  and  Rio  de  Janiero, 
which  were  formerly  famous  as  endemic  centers  of  the  disease, 
and  from  which  it  was  carried  to  seaports  in  all  parts  of  the  world, 
are  now  practically  free  from  it.  It  is  only  in  such  notoriously 
unsanitary  cities  as  Merida  in  Yucatan  and  Buenaventura  in 
Colombia  that  yellow  fever  still  rages,  with  little  or  no  attempt 
on  the  part  of  the  inhabitants  to  stamp  it  out. 

Nature  of  the  Disease.  —  Our  present  knowledge  of  the  nature 
of  yellow  fever  and  of  its  dissemination,  which  has  made  pos- 
sible the  scientific  checking  of  the  disease  and  will  undoubtedly 
result  ultimately  in  its  complete  extermination,  is  largely  the 
result  of  the  noble  and  self-sacrificing  work  of  the  American 
Yellow  Fever  Commission  appointed  in  1900,  consisting  of  Reed, 
Carroll,  Lazear  and  Agramonte.  Three  of  these  illustrious  men, 
Doctors  Lazear,  Reed  and  Carroll,  lost  their  lives  directly  or 
indirectly  as  the  result  of  their  work,  but  their  achievements  are 
of  inestimable  value  to  the  human  race  and  their  names  will 
not  soon  be  forgotten.  The  discovery  by  Noguchi  of  the  organism 
causing  the  disease  in  1918  has  opened  up  new  possibilities  in  the 
way  of  immunization. 

Yellow  fever  was  shown  by  the  American  Commission  to  be 
not  a  contagious  disease,  but  one  which  can  be  transmitted  only 
by  the  yellow  fever  mosquito,  Aedes  calopus,  or  by  injections  of 
blood  from  an  infected  person.  The  organism  causing  the  disease 
was  discovered  by  Noguchi  at  Guayaquil  in  1918,  and  was  found 
to  be  a  spirochsete-like  organism  closely  related  to,  and  very 
closely  resembling,  the  spirochaete  of  infectious  jaundice.  It 
was  named  by  Noguchi  Leptospira  icteroides.  The  organism  can 
be  found  in  the  blood  serum  and  also  in  the  tissues  of  the  liver, 
kidneys  and  other  organs.  It  has  been  obtained  in  pure  culture 
both  from  blood  of  patients  and  from  inoculated  animals.  It  is 
an  extremely  delicate  filament  varying  in  length  from  4  to  9  m,  and 
tapering  gradually  toward  the  extremities  which  end  in  immeas- 
urably thin  sharp  points.  The  filament  is  minutely  wound  at 
short  and  regular  intervals,  the  length  of  each  spiral  measuring 
about  one-fourth  of  a  micron.     The  windings  are  so  placed  as  to 


YELLOW  FEVER  71 

form  a  zigzag  line  by  the  alternate  right  angle  change  of  direction 
of  each  consecutive  spiral.  The  organism  is  smaller  than  that 
of  infectious  jaundice  and  is  actively  motile. 

Since  the  mosquitoes  cannot  transmit  the  disease  by  biting 
until  12  or  14  days  after  sucking  infected  blood  the  parasites 
evidently  undergo  a  cycle  of  development  in  the  mosquito.  The 
appearance  and  habits  of  the  yellow  fever  mosquito  are  described 
on  page  443. 

The  Disease.  —  Yellow  fever  has  an  incubation  period  of  from 
three  to  six  days.  The  first  symptoms  are  severe  headache  and 
aches  in  the  bones,  followed  by  a  sudden  fever  during  which 
the  face  is  flushed  and  swollen  and  the  skin  dry.  This  fever 
slowly  subsides,  and  after  three  or  four  days  there  is  a  period 
of  ''  calm  "  during  which  the  temperature  is  near  normal  but  the 
pulse  very  slow.  By  the  third  day  the  skin  usually  becomes  a 
characteristic  yellow  color,  which,  as  the  disease  progresses, 
changes  to  a  deep  coffee  brown.  A  striking  but  not  invariable 
symptom,  and  one  of  ill  omen,  is  the  "  black  vomit,"  a  gushing 
up  through  the  oesophagus  of  a  coffee-colored  or  even  black  fluid, 
consisting  largely  of  fragments  of  red  blood  corpuscles  and  freed 
haemoglobin,  and  sometimes  even  pure  blood.  The  period  of 
"  calm  "  may  lead  to  recovery  in  a  few  days  or  there  may  be  a 
second  fever  which  lasts  irregularly  for  a  longer  time  than  the  first. 

Yellow  fever  is  a  very  fatal  disease.  During  the  French  oper- 
ations at  Panama  relay  after  relay  of  laborers  were  stricken 
with  the  yellow  plague  and  were  turned  loose  to  die  without  mercy 
or  help,  to  be  replaced  by  a  new  set.  Not  only  the  laborers  but 
the  engineers,  nurses  and  others  were  stricken  down.  One  vessel 
is  reported  to  have  brought  over  18  young  French  engineers, 
all  but  one  of  whom  died  of  yellow  fever  within  a  month  after 
their  arrival. 

Fortunately  yellow  fever  gives  a  permanent  immunity  after 
one  attack  has  been  successfully  withstood.  In  children  the 
disease  is  often  very  mild  so  that  it  is  frequently  not  even  recog- 
nized, yet  the  immunity  it  gives  is  permanent.  Natural  im- 
munity is  unknown  in  any  race,  sex  or  age,  though  the  negroes 
suffer  less  from  the  disease  and  have  a  much  lower  per  cent  of 
mortality  than  the  whites. 

Treatment  and  Prevention.  —  Until  the  discovery  of  the  or- 
ganism causing  yellow  fever  by  Noguchi  and  its  isolation  in  pure 


72  SPIROCHETES 

culture,  the  treatment  of  yellow  fever  consisted  only  of  careful 
nursing  and  in  the  maintenance  of  the  best  hygienic  conditions: 
there  are  no  drugs  known  which  have  any  value  as  specifics 
against  the  disease.  Recently,  however,  Noguchi  and  his  fellow 
workers  at  the  Rockefeller  Institute  have  demonstrated  the 
development  of  antibodies  in  animals  and  man  inoculated  with 
killed  cultures  of  the  leptospira,  and  from  the  results  of  vaccin- 
ation in  guinea  pigs,  concluded  that  with  the  inoculation  of  a 
sufficient  quantity  of  dead  organisms  they  were  rendered  immune 
to  subsequent  infection.  Distinctly  encouraging  results  have  been 
obtained  from  the  vaccination  of  human  beings.  Of  8000  non- 
immune persons  vaccinated  in  tropical  America,  excluding  those 
exposed  to  the  disease  just  before  or  immediately  after  vaccin- 
ation, no  cases  of  yellow  fever  have  developed,  while  among 
unvaccinated  persons  during  the  same  period  and  in  the  same 
locality  there  have  been  about  700  cases  of  the  disease.  A  thera- 
peutic serum  has  also  been  prepared  for  treatment  of  yellow  fever. 
According  to  Noguchi  persons  treated  with  a  sufficient  quantity 
of  the  serum  before  the  third  day  of  illness  have  invariably  re- 
covered. By  the  fourth  day  of  illness  the  injuries  to  organs  are 
so  great  as  to  be  irreparable  in  severe  cases.  The  usual  50  to 
60  per  cent  mortality  from  yellow  fever  was  reduced  to  9  per  cent 
by  the  use  of  the  serum,  while  still  in  an  experimental  state. 

The  eradication  of  yellow  fever  consists  largely  in  the  applic- 
ation of  sanitary  measures  to  exterminate  the  yellow  fever  mos- 
quito Aedes  calopus,  but  in  the  face  of  an  epidemic  this  can  now 
be  supplemented  by  vaccination  to  cut  off  the  supply  of  non- 
immunes from  infected  mosquitoes.  According  to  Noguchi  a 
threatening  epidemic  in  Central  America  in  1920  is  reported  to 
have  been  checked  by  these  methods  within  a  month,  i.e.,  before 
the  development  of  the  second  set  of  cases.  The  value  of  im- 
munization as  an  emergency  measure  does  not,  however,  mini- 
mize the  importance  of  anti-mosquito  campaigns,  since  the  elimin- 
ation of  both  factors  —  non-immune  human  beings  and  infected 
mosquitoes  —  is  necessary  for  the  eradication  of  yellow  fever.  The 
habits  of  the  mosquito,  as  described  on  p.  444,  are  such  that  it  is  not 
difficult  to  combat  and  successful  campaigns  against  it,  with  a  re- 
sultant obliteration  of  yellow  fever,  have  been  made  in  many  places. 
Panama,  Havana,   Rio   de  Janiero,   and  recently  Manaos  and 


OTHER  SPIROCHETES  73 

Yquitos,  are  conspicuous  examples  of  tropical  cities  which  have 
been  cleared  of  the  disease  which  once  made  them  highly  dangerous 
to  visitors  and  a  menace  to  the  rest  of  the  world.  In  connection 
with  an  incessant  war  on  the  transmitting  mosquito  in  all  stages 
of  its  life  history,  all  known  or  suspected  cases  of  yellow  fever 
should  be  carefully  screened  so  that  mosquitoes  can  have  no  access 
to  them. 

Rat-bite  Fever 

In  many  parts  of  the  world,  especially  in  Japan,  there  occurs  a 
disease  which  follows  a  rat  bite,  and  is  therefore  known  as  "  rat- 
bite  fever."  It  has  been  reported  from  various  localities  in  the 
United  States.  Some  inflammation  occurs  at  the  place  of  the 
bite  and  the  neighboring  lymph  glands  swell  up.  After  several 
weeks  a  high  fever  ensues,  preceded  by  chills  and  headache. 
The  apparently  healed  rat  bites  become  inflamed  and  there  is 
usually  a  red  rash  which  spreads  all  over  the  body.  In  from  three 
to  seven  days  the  fever  subsides  but  it  recurs,  usually  within 
a  week,  with  similar  symptoms,  and  the  rash  is  more  constantly 
present  than  in  the  first  attack.  In  some  cases  there  are  still 
more  relapses. 

The  similarity  of  the  disease  to  such  spirochsete  diseases  as  the 
relapsing  fevers  is  obvious,  and  its  spirochsete  nature  was  long 
suspected  by  Japanese  physicians,  especially  when  they  found 
salvarsan  to  be  effective  in  its  treatment.  Within  the  past 
few  years  some  Japanese  physicians  (Futaki,  Takaki,  Taniguchi 
and  Osumi)  discovered  in  seven  out  of  eight  patients  numerous 
actively  moving  spirochsetes  in  the  broken-out  skin  and  in  swollen 
l3anph  glands.  Animals  were  successfully  inoculated  with  the 
disease  by  means  of  bits  of  skin  tissue  and  blood  containing  spiro- 
chsetes. The  organism,  which  has  been  named  Spirochceta  morsus 
muris,  is  described  as  being  an  actively  moving  animal,  larger 
than  Sp.  pallida  of  syphilis,  but  smaller  than  the  relapsing  fever 
spirochsetes.  It  is  rather  short  and  thick  with  an  attenuated 
portion  or  flagellum  at  each  end.  Long  spirochsetes,  at  first 
thought  to  be  specifically  distinct  from  the  short  thick  forms, 
also  are  found  in  human  infections.  According  to  Kaneko  and 
Okuda  these  are  probably  degenerate  forms  resulting  from  the 
action  of  antibodies. 

The  Japanese  investigators  have  been  unable  to  find  the  spiro- 


73a  spirochetes 

chaete  in  the  saliva  of  infected  rats  or  of  other  rodents,  but  only 
in  their  blood.  From  this  the  conclusion  has  been  drawn  that 
the  source  of  infection  in  a  rat  bite  is  blood  from  hemorrhages 
of  the  gums  or  tongue  which  contaminates  the  teeth. 

Both  mercury  and  salvarsan  are  effective  in  the  treatment  of 
this  disease  as  of  most  other  spirochsete  diseases. 

Attention  should  be  called  to  the  fact  that  rat  bites  may  often 
give  rise  to  diseases  which  may  be  of  quite  different  nature  from 
the  "  rat-bite  fever  "  described  above.  It  is  well  known  that 
many  different  infective  organisms  live  in  the  mouth  and  around 
the  teeth  of  such  animals  as  rats,  and  it  is  not  surprising  that 
infections  of  divers  kinds  may  result  from  rat  bites,  and  that 
these  infections  should  have  been  confused  with  typical  rat-bite 
fever.  Several  investigators  have  described  a  vegetable  organ- 
ism, Streptothrix,  as  the  cause  of  rat-bite  fever.  Recently  Ruth 
Tunnicliff  has  shown  that  a  form  of  pneumonia  in  rats  is  pro- 
duced by  a  Streptothrix  very  similar  to,  if  not  identical  with,  that 
described  in  some  cases  of  rat-bite  fever.  It  is  very  probable 
that  these  cases  were  really  infections  with  the  pneumonia-caus- 
ing organism,  and  quite  distinct  from  the  Japanese  disease. 

Other  Spirochsete  Diseases 

Spirochsetes,  often  in  association  with  bacteria  of  various  kinds, 
have  been  found  in  a  number  of  other  human  diseases,  and  are 
in  all  probability  at  least  partially  the  cause  of  them. 

The  common  spirochsete,  Sp.  huccalis,  which  lives  about  the 
gums  and  roots  of  the  teeth  in  almost  all  human  mouths  is 
thought  by  some  investigators  to  be  entirely  harmless,  living 
only  on  waste  matter.  By  others  it  is  thought  to  become 
pathogenic  under  some  circumstances,  and,  in  partnership  with 
certain  cigar-shaped  bacteria,  to  be  the  cause  of  Vincent's  angina, 
a  diphtheria-like  ulceration  of  the  tonsils  and  throat;  of  noma, 
an  ulceration  of  the  mouth  cavity  and  cheeks;  of  ulcerations  of 
the  nose,  teeth  and  lungs;  and  of  balanitis,  an  ulceration  of  the 
genital  organs  which  may  occur  after  unnatural  sexual  relations. 
In  central  America  there  is  a  common  disease  "  mal  de  boca  " 
(disease  of  the  mouth)  which  is  marked  by  swollen,  spongy  and 
tender  gums  over  which  a  whitish  pellicle  forms.  It  is  infectious 
and  is  probably  caused  by  a  delicate  spirochsete  found  on  the 


DISEASES  OF  MUCOUS   MEMBRANES  73b 

lesions.  Some  workers  believe  that  some  or  all  of  these  auctions 
are  due  to  difterent  species  of  spirochsetes  and  bacteria,  but  the 
fact  that  both  organisms  are  found  together  in  all  these  diseases, 
and  that  they  show  only  such  slight  differences  from  the  organ- 
isms in  the  mouth  as  would  be  expected  under  altered  conditions, 
makes  it  seem  quite  possible  that  Spirochceta  huccalis  and  its  con- 
stant companion,  a  cigar-shaped  bacterium,  are  the  causes  of 
all  of  them.  The  conditions  which  seem  to  favor  the  growth  and 
disease-producing  propensities  of  these  organisms  are  heat, 
moisture,  filth  and  absence  of  air.  Wherever  these  conditions 
prevail,  and  these  ordinarily  harmless  organisms  can  get  a  foot- 
hold, sores  and  ulceration  are  likely  to  result,  accompanied  by 
more  or  less  fever  and  digestive  disturbance  due  to  absorption 
of  poisonous  substances  from  the  decaying  tissues. 

The  treatment  of  these  affections  must  vary  with  their  location. 
For  the  sores  on  the  tonsils  or  mouth  cavity  in  Vincent's  angina  or 
noma  either  salvarsan  or  silver  nitrate  is  effective.  It  should  be 
daubed  on  the  injured  tissue  with  a  piece  of  cotton.  The  silver 
nitrate  is  less  dangerous  than  salvarsan  and  equally  effective  for 
these  superficial  ulcers.  Treatment  of  the  infected  parts  with 
a  two  per  cent  solution  of  silver  nitrate  for  a  few  days  results  in 
a  rapid  healing.  In  case  of  balanitis,  ordinary  cleanliness  and 
exposure  to  air  is  sufficient  to  cause  a  spontaneous  healing  in 
four  or  five  days.  Washing  with  hydrogen  peroxide,  which 
liberates  oxygen  in  the  presence  of  organic  matter,  is  very  de- 
structive to  such  organisms  as  these,  which  thrive  best  in  the 
absence  of  air. 

In  the  Sudan  region  of  Africa,  and  also  in  Colombia,  South 
America,  there  is  found  a  certain  type  of  bronchitis,  marked  by 
fever  and  often  by  hemorrhages  along  the  respiratory  tubes, 
which  is  accompanied  by  the  spirochse,  .  Sp.  hronchialis.  This 
parasite  has  very  slender  pointed  ends,  and  averages  eight  to 
nine  fj,  (^^jViy  of  a,n  inch)  in  length,  but  its  most  marked  charac- 
teristic is  its  variability.  These  spirochsetes  reproduce  by  the 
peculiar  method  of  *'  granule  shedding,"  breaking  up  into  tiny 
round  bodies  which  later  develop  into  new  spirochsetes.  It  is 
probable  that  these  little  particles  of  living  matter  can  resist 
drying  up  in  air,  especially  in  humid  atmospheres,  and  may  there- 
fore be  transmitted  with  dust  or  with  little  droplets  of  moisture 
propelled  by  coughing. 


73c  SPIROCH.ETES 

Tropical  Ulcer.  —  Still  another  human  disease  that  has  been 
attributed  to  spirochsetes  is  tropical  ulcer,  also  known  by  the 
more  impressive  name,  "  tropical  sloughing  phagedsena."  This 
is  a  type  of  sore  on  the  skin,  most  commonly  of  the  leg,  which 
originates  either  in  some  slight  abrasion  of 
the  skin  or  in  some  preexisting  wound  or 
sore,  especially  in  persons  debilitated  by 
some  other  disease  or  by  alcohol.  It  begins 
in  a  tiny  blister  which  soon  bursts,  and  the 
sore  thus  exposed  spreads  very  rapidly,  con- 
stantly sloughing  a  yellowish,  moist  and 
exceedingly  fetid  matter.    After  a  few  days, 

Fig.  13.    Tropical  ulcer.        ,  -i      ,-,  •        ,'^^  ■,•  ,,  . 

(Drawn  from  photo  by  while  the  sore  IS  Still  spreadmg,  the  center 
Haiberstadter  in  KoUe  of  the  slough  begins  to  liquefy  and  is  grad- 
and  Wassermann.)  ^^^^^  sloughed  off  and  heals.     Usually  the 

ulceration  confines  itsQlf  to  the  skin  but  sometimes  it  goes  deep 
into  the  muscles,  nerves  and  bloodvessels,  even  injuring  the 
bones  and  joints.  Sometimes  permanent  deformity  or  even 
death  results  from  these  extensive  excavations,  death  resulting 
especially  from  the  opening  of  some  large  bloodvessel. 

Tropical  ulcer  occurs  in  nearly  all  hot  damp  tropical  countries. 
Although  not  definitely  proved,  it  is  usually  accepted  that  the 
spirochsetes,  Spirochoeta  schaudinni,  which  can  almost  always  be 
found  in  the  ulcers,  together  with  cigar-shaped  bacteria  found  in 
association  with  them,  are  the  ringleaders  in  producing  it.  The 
treatment  usually  recommended  is  a  thorough  cauterization  of 
the  sore,  followed  by  antiseptic  washes  and  applications.  Sal- 
varsan  and  other  arsenic  compounds  have  been  found  beneficial 
in  many  cases.  Finocchiaro  and  Migliano  in  Brazil  claim  to 
have  found  a  specific  cure  for  this  loathsome  disease  in  an  appli- 
cation of  powdered  permanganate  of  potash  or  in  a  compress  of  a 
one  to  ten  solution  of  this  substance.  They  achieved  a  complete 
cure  in  from  ten  to  thirty  days  in  every  one  of  seven  cases. 

Ulcerating  Granuloma.  —  Of  a  somewhat  similar  nature  to 
tropical  ulcer,  and  of  wide  distribution  in  the  tropics,  is  ''  ulcerating 
granuloma  of  the  pudenda,"  a  sore  which  spreads,  very  slowly 
however,  over  the  external  genitals  and  along  the  moist  folds 
of  skin  in  neighboring  regions.  Both  spirochsetes  and  bacteria 
have  been  found  deeply  situated  in  the  tissues  at  the  bases  of 
these  sores,  but  to  what  extent  either  or  both  are  responsible  for 


PATHOGENICITY  73d 

the  condition  is  not  known.  The  disease  is  pecuHar  in  being 
very  refractory  to  treatment  by  any  of  the  usual  methods  of 
cauterization  or  appUcation  of  drugs.  Recently,  however,  it 
has  been  found  to  succumb  to  X-ray  treatment,  and  this  method 
is  now  extensively  employed.  A.ragao  and  Vianna  in  Brazil 
and  Breinl  and  Priestley  in  Australia  have  obtained  excellent 
results  from  intravenous  injections  of  tartar  emetic. 

Japanese  Seven-Day  Fever.  —  A  number  of  Japanese  workers 
have  recently  described  this  disease  as  resembling  infectious 
jaundice  but  usually  without  the  occurrence  of  jaundice.  It  has 
a  fairly  wide  distribution  in  Japan  among  field  workers.  A 
spirochaete  morphologically  indistinguishable  from  Leptospira  ic- 
ier ohcemorrhagice,  but  distinct  in  its  immune  reactions,  has  been 
found  in  blood  and  urine  of  human  cases,  and  in  inoculated 
animals.  The  organism  was  named  Spirochceta  hebdomadis,  but 
if  related  to  the  organism  of  infectious  jaundice  should  be  called 
Leptospira  hehdomadis.  A  spirochaete  believed  to  be  identical 
with  this  was  found  in  the  field  mouse,  Microtus  montehelli, 
and  the  Japanese  believe  that  this  mouse  acts  as  a  reservoir  for 
the  disease  as  does  the  rat  for  infectious  jaundice. 

Other  Spirochaetes.  —  Spirochsetes  have  been  found  in  con- 
nection with  still  other  human  afflictions,  and  it  is  possible  that 
they  may  be  the  cause  of  them.  In  most  cases,  however,  it  is 
more  probable  that  spirochsetes  which  are  normally  harmless  and 
Hve  only  on  dead  matter  find  congenial  surroundings  in  tissues 
diseased  by  some  other  cause,  and  that  this  accounts  for  their 
presence.  Often,  however,  such  ordinarily  harmless  spirochajtes 
may  change  their  habits  under  suitable  conditions  and  become 
pathogenic,  thus  aggravating  the  diseased  condition.  The  patho- 
genic propensities  of  spirochsetes  have  been  demonstrated  in  so 
many  cases,  however,  that  they  may  rightly  be  looked  upon  as 
one  of  the  most  destructive  groups  of  human  parasites. 


CHAPTER  V 

LEISHMAN  BODIES  AND  LEISHMANIASIS 

Leishman  Bodies  in  General.  —  While  investigating  the  cause 
of  a  deadly  disease  of  tropical  India  known  to  the  natives  as 
kala-azar  or  dumdum  fever,  Leishman,  in  1903,  and  at  about  the 
same  time,  Donovan,  discovered  in  the  spleen  of  victims  numerous 
little  round  parasites.  These  looked  to  Leishman  exactly  like  the 
non-flagellated  stage  of  a  trypanosome  (see  Chapter  VI),  and  he 
naturally  took  them  to  be  developmental  stages  of  trypanosomes, 
and  added  another  terrible  disease  to  the  credit  of  those  murder- 
ous animals.  Later,  however,  it  was  found  that  while  these  little 
round  organisms  resemble  a  certain  stage  in  the  life  history  of  a 
trypanosome,  yet  they  never  reach  this  fully  developed  form. 
Nevertheless  it  was  discovered  that  when  transferred  to  the  in- 
testine of  certain  insects,  or  when  grown  on  artificial  cultures, 
they  undergo  a  wonderful  transformation.  They  become  elon- 
gate in  form  and  develop  a  waving  flagellum,  assuming  what  is 
known  as  a  *'  Herpetomonas  "  form  (see  Fig.  14L),  and  they  move 
about  so  actively  that  it  is  difficult  to  believe  that  they  are  really 
transformed  from  the  un-animal-like  round  bodies  found  in 
diseased  human  bodies.  Such  flagellates,  under  the  name  "  Lep- 
tomonas  "  or  "  Herpetomonas/^  had  been  known  before,  and  were 
recognized  as  common  parasites  of  insects,  belonging  to  a  primi- 
tive group  of  the  class  Flagellata.  They  were  also  known  to 
present,  during  their  development,  this  unflagellated  round 
condition,  but  always  in  the  bodies  of  insects.  Here  was  a 
vicious  form  of  the  parasite  which  was  not  content  with  life  in  an 
insect,  but  must  adapt  itself  to  live  in  the  bodies  of  warm-blooded 
animals.  There  is  reason  to  believe  that  some  of  the  flagellates 
which  normally  live  exclusively  in  the  intestines  of  blood-sucking 
insects  have  the  power,  if  injected  into  warm-blooded  animals, 
to  adapt  themselves  to  the  conditions  they  find  there,  causing 
more  or  less  local  inflammation  and  sores.  In  Panama,  for 
instance,  sporadic  cases  of  sores  occur  in  which  are  found  Leish- 

74 


H^MOFLAGELLATA  75 

man  bodies  in  small  numbers,  resulting  from  the  bite  of  horse- 
flies (Tabanidae)  of  various  species.  There  is  every  reason  to 
believe  that  the  parasites  in  these  sores  are  normally  parasitic 
in  the  insects  only,  but  are  able  to  adapt  themselves  to  their  new 
environment  in  human  flesh  and  to  multiply  there  for  a  time. 
They  are  permanently  sidetracked,  however,  and  have  no  further 
chance  of  completing  their  life  history  or  of  reaching  new  hosts, 
unless  a  suitable  fly  should,  by  some  infinitesimally  small  chance, 
suck  blood  from  the  sore  in  which  they  were  developing,  and  thus 
rescue  them. 

Several  investigators  have  recently  shown  that  a  number  of 
typical  insect  flagellates,  if  injected  into  mice  and  rats  or  other 
mammals,  or  even  birds,  may  become  pathogenic  and  even 
cause  the  death  of  the  animal.  That  the  well-established  Leish- 
mania  diseases  of  man  and  other  animals  originated  from  insect 
flagellates  can  hardly  be  doubted,  but  it  is  possible  that  in  some 
cases  the  parasites  may  have  adapted  themselves  to  their  new 
type  of  host  to  such  an  extent  as  to  have  become  quite  independ- 
ent of  the  insects  from  which  they  originated.  Fantham  suggests 
that  all  forms  of  Leishmania  and  Herpetomonas  may  be  mere 
physiological  races  of  a  single  species  which  is  variously  adapted 
to  live  in  a  variety  of  different  hosts,  and  perhaps  able  to  adapt 
itself  anew  to  unaccustomed  hosts  under  certain  conditions. 

Leishmania  and  Herpetomonas  belong  to  a  group  of  the  class 
Flagellata  known  as  the  Hsemoflagellata.  This  group  presents 
a  series  of  forms  from  the  simple  Leishmania,  which  at  times  is 
a  non-motile,  unflagellated  organism,  through  the  increasingly 
highly  developed  Herpetomonas  and  Crithidia  to  the  trypano- 
somes  (see  Fig.  18).  Some  reach  only  the  Herpetomonas  stage  as 
adults,  others  only  the  Crithidia  stage,  while  others  pass  through 
the  entire  series  of  developmental  stages  and  reach  the  final 
trypanosome  stage.  All  of  them  are  probably  primarily  parasites 
of  the  guts  of  insects  or  other  invertebrates,  and  only  compara- 
tively few  of  them  have  adapted  themselves  to  spending  part 
of  their  existence  in  the  blood  or  tissues  of  vertebrates.  Ap- 
parently only  the  Leishmania  and  trypanosome  forms  are 
adapted  for  existence  in  vertebrates,  since  the  other  forms  are 
not  found  in  them,  except  in  rare  instances  when  Herpetomonas 
forms  are  found  in  the  blood  of  Le^^s/imama-infected  individuals. 
A  number  of  species  have  become  thoroughly  adapted  to  life  in 


76  LEISHMAN  BODIES  AND  LEISHMANIASIS 

vertebrates  and  are  now  normal  parasites  of  them,  and  others, 
as  already  shown,  if  accidentally  introduced  may  be  able  to 
multiply  sufficiently  to  cause  local  or  temporary  sores,  or  even  a 
fatal  infection. 

All  the  species  of  hsemoflagellates  which  normally  live  in  warm- 
blooded animals  in  the  form  of  Leishman  bodies  are  grouped 
together  in  the  genus  Leishmania.  A  number  of  human  diseases 
are  known  to  be  caused  by  them.  Kala-azar  of  southern  Asia, 
already  mentioned,  is  the  most  severe  one.  A  similar  disease, 
infantile  kala-azar,  occurs  around  the  Mediterranean,  especially 
in  children.  There  are  also  a  number  of  Leishmanian  diseases 
which,  instead  of  causing  constitutional  disturbances,  cause  sores 
or  ulcers  on  the  skin  or  mucous  membrane.  One  type,  oriental 
sore,  also  called  by  various  local  names,  is  widespread  throughout 
many  tropical  countries,  especially  southern  Asia  and  around  the 
eastern  end  of  the  Mediterranean,  and  possibly  in  tropical  South 
America.  It  causes  temporary  sores  on  the  skin,  chiefly  of  the 
exposed  parts  of  the  body;  the  sores  may  or  may  not  ulcerate. 
In  South  America  there  occurs  a  much  more  vicious  type  of 
the  disease  in  which  the  skin  sores  are  followed  by  ulcers  spreading 
over  extensive  areas  of  the  mucous  membranes  of  nose  and  mouth, 
often  resulting  fatally.  A  parasite,  Aphthomonas  infestans,  be- 
lieved to  be  aUied  to  Leishmania,  has  recently  been  described  by 
Stauffacher  as  the  cause  of  foot-and-mouth  disease. 

The  clinical  manifestations  of  these  ulcers  and  sores  on  the  skin 
or  mucous  membranes  are  extremely  variable  and  indicate  the 
possibility  of  there  being  a  number  of  different  species  or  at  least 
varieties  of  Leishmania  causing  them.  There  are  some  parasi- 
tologists who  believe  that  all  the  different  kinds  of  Leishmani- 
asis —  internal,  cutaneous  or  mucosal  —  are  caused  by  different 
strains  of  the  same  species,  while  others  believe  in  the  existence 
of  several  species.  Usually  four  species  are  recognized,  as  fol- 
lows: Leishmania  donovani,  causing  kala-azar;  L.  infantum, 
causing  infantile  leishmaniasis;  L.  tropica,  causing  cutaneous 
sores;  and  L.  americana  (hrasiliensis) ,  causing  sores  or  ulcers  of 
long  duration  on  the  skin  and  mucous  membranes.  However, 
until  we  are  familiar  with  the  adult  forms  of  all  the  various  types 
of  Leishmania,  and  know  more  about  their  life  histories,  we  can 
only  guess  at  their  classification. 


KALA-AZAR  77 


Kala-azar 


About  1870  there  began  a  great  epidemic  of  a  strange  and 
deadly  disease  in  Assam,  India,  which  spread  up  through  the 
Brahmaputra  Valley.  It  was  believed  to  have  been  imported 
by  the  British  from  Rangpur,  where  a  similar  epidemic  had  been 
raging  for  some  time  before.  Whole  villages  and  settlements 
were  depopulated  and  the  country  was  terrorized  by  the  ''  black 
sickness."  It  is  said  that  victims  of  the  disease  were  driven  out 
of  the  villages,  sometimes  being  made  unconscious  with  drink, 
taken  into  the  jungle,  and. burnt  to  death.  Some  villages  com- 
pletely isolated  themselves  from  the  outside  world,  and  still 
others  were  entirely  deserted  for  new  and  uninfected  districts. 
The  natives  were  most  severely  affected,  no  doubt  due  both  to 
their  filthiness  and  unsanitary  habits  and  to  their  weak  con- 
dition as  the  result  of  almost  universal  malaria  ^  .1  hookworm. 
Before  the  true  nature  of  the  disease  was  discovered  it  was  usu- 
ally diagnosed  as  ''severe  malaria";  one  physician  concluded 
that  it  was  excessive  hookworm  infection,  since  he  found  hook- 
worms almost  universally  present  in  kala-azar  sufferers. 

This  Assam  epidemic,  which  lasted  for  many  years,  is  the  only 
recent  case  of  a  great  epidemic  of  kala-azar,  although  the  disease 
now  occurs  endemically  in  many  parts  of  India  and  Southern 
China,  and  is  spreading  in  the  Sudan  region  of  North  Africa. 
It  has  been  pointed  out  that  the  endemic  parts  of  China,  chiefly 
along  the  north  bank  of  the  Yangtse  River  and  its  tributaries, 
correspond  closely  in  latitude  and  climate  to  a  considerable  part, 
of  southern  United  States,  and  since  kala-azar  is  believed  by  some 
to  be  spread  by  bedbugs  and  perhaps  other  vermin,  there  is  danger 
that  once  introduced  it  might  become  endemic  in  America. 
A  single  case  has  been  found  in  Brazil,  contracted  in  a  region 
where  another  form  of  Leishmaniasis  is  prevalent.  How  this 
case  should  be  explained  is  difficult  to  know. 

Transmission.  —  In  spite  of  numerous  experimental  investiga- 
tions to  discover  the  mode  of  transmission  of  the  kala-azar  para- 
site, Leishmania  donovani,  the  question  is  still  obscure.  Captain 
Patton,  of  the  British  Medical  Service  in  India,  adduced  some 
evidence  that  the  common  Indian  bedbug,  Cimex  hemipterus 
{rotundatus)  J  is  the  normal  intermediate  host  and  transmitter 
of  kala-azar.     Using  laboratory-bred  bugs,  Patton  succeeded  in 


78  LEISHMAN  BODIES  AND  LEISHMANIASIS 

getting  abundant  growths  of  the  parasites  in  the  intestines  of 
the  bugs  after  they  had  been  fed  on  infected  blood.  When 
sucked  up  by  the  bugs,  the  Leishmania-laiden  cells  in  the  blood  are 
digested  and  the  parasites  set  at  liberty  in  the  stomach.  Here 
after  several  days  they  begin  to  go  through  their  remarkable 
transformations  and  active  flagellated  Herpetomonas  forms  de- 
velop similar  to  those  which  occur  in  artificial  cultures  (Fig.  14, 
F  to  0).  After  several  days  of  free  active  life  the  parasites 
round  up  again,  lose  their  flagella,  and  are  then  presumably 
ready  for  inoculation  into  a  new  host.  All  these  changes  occur 
during  a  period  of  12  days.  Patton  has  not,  however,  shown 
that  the  bedbug  is  capable  of  transmitting  the  parasites  to  other 
victims  by  means  of  its  bites,  though  it  is  possible  that  scratching 
of  the  bites  and  crushing  of  the  bugs  might  cause  infection. 
Developmental  stages  have  also  been  traced  in  the  mosquito. 
Anopheles  punctipennis,  but  here  again  there  is  no  proof  of  the 
insect's  method  or  power  of  transmitting  the  parasites  to  new 
hosts.  The  facts  connected  with  the  spread  of  the  disease  in 
India  seem  to  favor  the  theory  of  transmission  by  a  household 
insect.  Rarity  of  the  parasites  in  the  circulating  blood  has  been 
claimed  as  an  argument  against  the  insect  transmission  theory, 
but  Patton  has  shown  that  almost  every  smear  of  blood  from  an 
infected  person  contains  white  blood  corpuscles  with  the  Leish- 
man  bodies  in  them.  On  the  other  hand  the  manner  of  spreading 
of  the  disease  in  Sudan  is  rather  opposed  to  a  theory  of  insect 
transmission,  and  it  has  been  suggested  that  infection  may  take 
place  through  the  medium  of  contaminated  water  or  food,  since 
experimental  animals  occasionally  become  infected  when  fed  on 
infected  material.  The  suggestion  is  also  made  that  an  intestinal 
wound  of  some  kind  may  be  necessary  to  allow  the  entrance  of 
parasites  into  the  blood  and  organs  of  the  body.  Bodies  re- 
sembling Leishman  bodies  have  been  found  in  the  faeces  of  in- 
fected persons,  so  that  faeces  may  in  some  way  have  to  do  with 
the  transmission  of  the  parasites.  The  difficulty  experienced  in 
inoculating  the  disease  into  experimental  animals  makes  the 
investigation  of  its  transmission  very  difficult.  The  parasites 
develop  readily  in  artificial  cultures  at  relatively  low  tempera- 
tures, presenting  the  series  of  changes  shown  in  Fig.  14.  These 
forms  are  practically  identical  with  those  found  by  Patton  in  the 
intestine  of  the  bedbug  and  undoubtedly  represent  part,  at  least, 


PARASITE  OF  KALA-AZAR 


79 


of  a  possible  cycle  in  an  insect  host.  That  this  phase  of  the 
life  history  of  the  parasite  may  normally  be  omitted  is  never- 
theless quite  possible. 

Human  Cycle.  —  After  entering  the  human  body,  the  para- 
sites probably  utilize  the  blood  and  lymph  streams  to  obtain 
transportation  to  all  parts  of  the  body,  but  do  not  live  free  in 


Fig.  14.  Parasites  of  kala-azar,  Leishmania  donovani;  A,  isolated  parasites 
from  spleen;  B,  dividing  forms  from  liver  and  bone  marrow;  C,  spleen  cell  with 
parasites;  Z),  group  of  cells  with  parasites;  E,  parasite  ingested  by  leucocyte;  F-0, 
from  cultures;  F  and  G,  early  stages  after  ingestion;  H,  large  dividing  forms;  /, 
development  of  flagellum;  J,  small  flagellated  form;  K  and  L,  flagellated  Herpe- 
tomonas  forms;  M  and  A^,  unequal  division;  0,  parasites  resulting  from  unequsU 
division  shown  in  M  and  A^".      X  about  1500.      (After  Leishman.) 


80  LEISHMAN  BODIES  AND  LEISHMANIASIS 

the  body  fluids.  They  enter  the  deUcate  endothehal  cells  which 
Hne  the  blood  and  lymph  vessels,  and  also  the  cells  of  the  spleen, 
liver  and  lymph  glands.  Within  the  cell  they  have  entered 
they  grow  and  multiply  rapidly  (Fig.  14C  and  D).  The  indi- 
vidual parasites  (Fig.  14A)  are  exceedingly  small,  about  two  ii 
(less  than  7^7^  of  an  inch)  to  four  /^  in  diameter.  They  are 
round  or  oval  in  form  with  a  large  nucleus  and  a  smaller  para- 
basal body  shaped  like  a  little  rod  and  set  more  or  less  at  a  tan- 
gent to  the  nucleus. 

In  a  short  time,  by  dividing  and  re-dividing,  the  Leishman 
bodies  completely  fill  the  cell  they  inhabit,  causing  it  to  enlarge  to 
many  times  its  normal  size  (Fig.  14C).  There  may  be  as  many 
as  several  hundred  parasites  in  a  single  enlarged  cell.  The 
parasitized  endothelial  cells  often  seem  to  "  run  amuck,"  breaking 
loose  from  their  normal  position  on  the  lining  of  bloodvessels 
and  becoming  free-living  carnivorous  cells  like  the  white  blood 
corpuscles.  When  these  parasite-filled  cells  finally  burst,  the 
liberated  parasites  enter  new  cells,  or  are  gobbled  up  by  the 
white  blood  corpuscles  (Fig.  14E).  It  is  probable  that  the  para- 
sites are  ingested  by  bedbugs  while  inside  free  endothehal  cells 
or  white  corpuscles  in  the  blood. 

The  Disease.  —  The  incubation  period  of  kala-azar  after  in- 
fection is  not  definitely  known,  but  Manson  cites  one  case  where 
an  Englishman  was  attacked  by  a  fever,  which  terminated  in 
kala-azar,  within  ten  days  after  arriving  in  an  endemic  locality. 

A  high  fever  usually  marks  the  onset  of  the  disease,  and  this 
persists  more  or  less  irregularly  for  several  weeks.  Meanwhile 
the  spleen  and  liver  enlarge  enormously,  increasing  and  decreas- 
ing with  the  fluctuations  of  the  fever.  After  several  weeks  the 
fever  drops  and  the  patient  becomes  almost  normal  for  some 
time,  only  to  be  attacked  by  the  fever  again,  with  an  enlargement 
of  spleen  and  liver.  These  remittent  attacks  gradually  dwindle 
to  the  steady  low  fever,  accompanied  by  sweating  spells,  rheu- 
matism-like aches,  high  pulse  rate,  anemia  and  a  general  wasting 
away,  with  the  skin  often  a  dark  earthen  color.  Dysenteric 
symptoms,  with  discharges  of  blood  and  mucus,  are  common, 
especially  in  the  late  stages  of  the  disease,  and  frequently  after 
death  the  intestine  is  found  to  be  extensively  ulcerated,  with 
numerous  parasites  in  the  walls  of  the  ulcers.  Parasites  are 
usually  found  most  abundantly  in  the  spleen,  liver  capillaries, 


TREATMENT  OF  KALA-AZAR  81 

bone  marrow  and  lymph  glands.  When  the  chronic  condition 
is  reached  the  patient  presents  an  appearance  not  unlike  that 
resulting  from  chronic  malaria,  and  it  is  little  wonder  that  the 
diseases  were  long  confused.  Usually  complication  by  some 
other  disease,  especially  dysentery,  which  gets  a  severe  hold  on 
account  of  the  low  vitality  of  the  victim,  causes  death  (accord- 
ing to  Rogers  in  96  per  cent  of  cases),  but  in  a  relatively  small 
per  cent  of  cases  there  is  recovery.  A  steady  gain  in  weight, 
however  slight,  is  said  by  Mackie  to  be  a  fairly  accurate  sign  of 
recovery. 

Treatment.  —  Within  the  past  few  years  (1914-1921)  the 
remarkable  destructive  effect  of  antimony,  especially  in  the  form 
of  tartar  emetic,  on  Leishman  bodies  has  been  thoroughly  es- 
tablished. Tartar  emetic  as  a  cure  for  Leishmanian  diseases 
was  first  tried  out  in  1912  with  astonishing  success  by  Vianna, 
a  Brazilian  investigator,  on  the  Leishmanian  ulcers  of  the  face 
and  nasal  mucosa.  Similar  treatment  has  been  applied  with 
equal  success  to  oriental  sores  and  to  infantile  kala-azar.  Its 
application  to  the  more  severe  Indian  kala-azar  has  been  attended 
with  great  success,  and  even  advanced  stages  of  the  disease  can 
sometimes  be  cured  by  its  use.  Rogers  and  Hume  have  used 
it  extensively  in  India.  Injections  of  metallic  antimony  have 
also  been  found  of  great  benefit  in  treatment  of  this  disease. 

The  usual  method  of  giving  tartar  emetic  is  by  injections  into 
the  veins,  as  in  trypanosome  diseases.  From  one  to  ten  cc.  of  a 
one  per  cent  solution  is  given,  the  dose  being  gradually  increased 
in  accordance  with  the  age  and  tolerance  of  the  patient.  The 
drug  is  a  powerful  one,  and  if  given  in  over-doses  may  cause 
severe  disturbances  of  the  digestive  tract  and  of  the  kidneys,  but. 
if  it  is  given  in  small  quantities  to  begin  with,  and  its  effects 
carefully  watched  as  the  doses  are  increased,  it  can  be  used  with- 
out danger  and  constitutes  a  treatment  as  specific  in  its  effects 
as  is  quinine  on  malarial  parasites,  or  salvarsan  on  spirochsetes. 

Prevention.  —  On  account  of  the  uncertainty  which  exists  con- 
cerning the  mode  of  transmission  of  kala-azar,  victims  of  the 
disease  and  those  who  have  closely  associated  with  them  should 
be  quarantined  and  their  houses  thoroughly  disinfected  to  kill 
any  bedbugs  or  other  vermin,  as  well  as  any  Leishman  bodies 
which  might  exist  in  any  body  excretions.  The  safest  method 
in  the  case  of  the  native  huts  which  are  hopelessly  filthy  and 


82  LEISHMAN  BODIES  AND  LEISHMANIASIS 

unsanitary  is  to  burn  them  with  all  their  junk.  This  method  of 
stamping  out  the  disease  before  it  has  had  time  to  spread  has 
been  successfully  used  on  some  of  the  tea  estates  in  Assam. 
For  the  successful  prevention  of  the  spread  of  the  disease,  an 
isolation  of  300  to  400  yards  has  been  found  sufficient,  a  fact 
which  exonerates  most  flying  insects  as  transmitters.  Houses  in 
endemic  regions  should  be  kept  scrupulously  free  from  bedbugs, 
and  any  place  where  bugs  might  be  acquired  should  be  care- 
fully avoided. 

Since  the  parasites  have  been  shown  to  exist  in  the  faeces  of 
infected  persons,  careful  and  thorough  disposal  of  the  faeces 
should  be  attended  to.  The  possibility  exists  that  non-blood- 
sucking flies  which  frequent  human  faeces  may  be  instrumental 
in  spreading  infection.  Until  proved  otherwise,  precautions 
against  this  should  be  taken  in  endemic  places. 

Infantile  Kala-azar 

In  many  of  the  countries  bordering  the  Mediterranean — Algeria, 
Tunis,  Malta,  Crete,  Greece,  southern  Italy,  Sicily,  Spain  and 
other  regions  —  there  occurs  a  disease  which  in  many  respects 
closely  resembles  true  kala-azar,  but  differs  from  it  very  strikingly 
in  other  ways.  While  true  kala-azar  attacks  young  and  old 
alike,  the  Mediterranean  disease  attacks  infants  and  children 
almost  if  not  quite  exclusively.  Children  between  one  and  two 
years  old  are  most  frequently  subject  to  it,  while  children  over 
six  years  old  are  practically  exempt.  While  true  kala-azar  is 
not  readily  communicable  to  other  animals  than  man,  the  Medi- 
terranean disease  occurs  naturally  in  the  dogs  of  endemic  regions 
and  in  some  places  where  the  disease  is  not  known  to  occur  in 
children.  It  can  be  experimentally  transmitted  not  only  to 
dogs  but  also  to  rats,  mice  and,  with  more  difficulty,  to  monkeys. 
Cats  cannot  be  successfully  inoculated.  It  is  believed  by  some 
that  the  disease  in  dogs  is  different  from  that  in  children,  but  the 
similarity  in  symptoms,  and  geographic  distribution,  as  well  as 
the  fact  that  dogs  can  be  infected  by  parasites  from  human 
beings,  and  other  dogs  from  these  dogs,  all  point  to  the  identity 
of  the  diseases. 

Transmission.  —  A  remarkable  fact  connected  with  artificial 
inoculation  of  the  disease  is  the  great  quantity  of  infective  ma- 


TRANSMISSION  OF  INFANTILE  KALA-AZAR  83 

terial  which  is  necessary  to  produce  infection.  Injection  of 
infected  material  under  the  skin  does  not  transmit  the  disease, 
although  in  nature  this  is  probably  the  mode  of  transmission. 
Evidently,  then,  the  natural  means  of  transmission  must  be  by 
more  powerful  or  virulent  parasites  than  can  be  obtained  from 
already  infected  animals.  The  common  opinion  is  that  the  dog 
flea,  Ctenocephalus  cams  (see  p.  416),  is  the  usual  transmitting 
agent,  and  that  this  insect  serves  as  an  intermediate  host  for  the 
parasites.  This  opinion  is  based  on  the  fact  that  parasites  ap- 
parently identical  with  those  in  infected  children  have  been 
found  in  the  tissues  and  faeces  of  fleas.  Brumpt,  however,  be- 
lieves that  there  has  been  confusion  with  an  apparently  harmless 
flagellate  which  is  frequent  in  fleas  even  where  infantile  kala-azar 
does  not  occur.  Patton  suggests  that  the  kala-azar  of  dogs  may 
really  be  an  infection  quite  distinct  from  the  infantile  disease  and 
caused  by  infection  with  the  common  intestinal  flagellate  of  fleas, 
Herpetomonas  ctenocephali.  The  possibility  that  the  human  dis- 
ease may  also  be  caused  by  this  flagellate  seems  to  have  been 
overlooked;  the  fact  that  the  fleas  do  not  readily  become  in- 
fected from  sucking  an  infected  child  does  not  necessarily  argue 
against  the  origin  of  the  human  parasites  from  fleas.  Recent 
work  by  da  Silva  and  Spagnolio  in  attempting  to  infect  fleas  by 
allowing  them  to  feed  on  a  naturally  infected  child  has  been  un- 
successful. They  fed  25  fleas  on  an  advanced  case  of  the  disease 
and  secured  no  infection  of  the  fleas  in  484  feeds.  These  authors 
do  not  believe  in  the  relation  of  fleas  to  infantile  kala-azar,  and 
point  out  that  the  disease  is  at  its  height  in  the  spring  before 
fleas  have  become  very  abundant. 

Infection  of  bedbugs  with  Leishmania  infantum  is  not  suc- 
cessful. If  fleas  do  serve  as  the  usual  transmitting  agents,  it  is 
probable  that  after  development  in  the  flea  the  Leishman  bodies, 
as  suggested  above,  become  more  resistant  and  are  able  to  establish 
themselves  in  situations  where  they  would  otherwise  be  destroyed 
before  they  had  a  chance  to  multiply  and  adapt  themselves. 

Since  so  many  dogs  around  the  Mediterranean  are  infected, 
although  only  a  small  number  give  any  indication  of  it,  they 
probably  serve  as  a  reservoir  for  the  disease.  Not  infrequently 
children  attacked  by  kala-azar  have  been  known  to  have  played 
with  diseased  dogs,  and  it  is  easy  to  see  how  the  fleas  which 
almost  always  infest  dogs  in  these  regions  could  infect  children. 


84  LEISHMAN  BODIES  AND  LEISHMANIASIS 

The  Disease.  —  The  disease  is  much  Hke  true  kala-azar  in 
most  of  its  chnical  manifestations,  though  differing  in  details. 
It  is  characterized  by  fever,  aches  and  anemia,  and  by  excessive 
enlargement  of  the  spleen,  the  liver  also  enlarging  somewhat. 
Though  in  some  places  comparatively  mild,  in  others  it  is  ex- 
tremely fatal.  Recovery  is  rarer  the  younger  the  patient;  in  130 
cases  reported  from  Palermo  and  Naples,  93  per  cent  of  the  chil- 
dren under  two  years  old  succumbed  to  it,  while  87  per  cent  of 
the  older  children  died.  Similar  high  mortality  has  been  re- 
ported in  other  parts  of  Italy. 

Usually  after  recovery  from  a  single  attack  immunity  is  given, 
almost  always  lasting  until  the  susceptible  age  is  passed. 

Treatment  and  Prevention.  —  Wonderfully  successful  results 
have  been  obtained  in  the  treatment  of  infantile  kala-azar  with 
tartar  emetic  as  described  on  page  81.  Of  eight  children  treated 
with  tartar  emetic  in  Italy,  all  of  whom  were  between  five  and 
27  months  old,  except  one  boy  of  six  years,  seven  recovered  com- 
pletely. In  the  last  stages  of  the  disease  the  vitality  is  so  weak- 
ened that  recovery  is  impossible  even  with  the  destruction  of  all 
the  parasites. 

Prevention  obviously  lies  in  keeping  infected  dogs  away  from 
children.  In  endemic  regions  dogs  should  be  kept  scrupulously 
free  from  fleas,  and  all  dogs  showing  the  slightest  symptoms  of 
feverishness,  enlarged  spleen  or  emaciation  should  be  killed,  and 
their  bodies  burned  to  destroy  fleas.  Even  if  this  were  done  it 
would  not  be  sufficient  to  stamp  out  the  disease  completely,  since 
so  many  dogs  carry  the  infection  in  latent  condition,  serving  as 
a  reservoir  for  it  without  showing  any  appreciable  symptoms. 
Basile  showed  the  value  of  attacking  the  disease  in  dogs  by  de- 
stroying all  obviously  infected  dogs  in  a  certain  township  in 
Italy.  In  the  year  the  dogs  were  destroyed  there  were  seven 
new  cases  of  the  disease  in  children  in  a  population  of  2000,  but 
in  the  following  year  not  a  single  new  case  appeared,  and  in  the 
year  after  only  one. 

Oriental  Sore 

One  of  the  commonest  sights  in  many  tropical  cities,  particu- 
larly in  the  cities  of  the  eastern  Mediterranean  region  and  south- 
western Asia,  is  the  great  number  of  children,  usually  under  three 
years  of  age,  who  have  on  the  exposed  parts  of  their  bodies  un- 


OCCURRENCE  OF  ORIENTAL  SORE 


85 


sightly  ulcerating  sores,  upon  which  swarms  of  flies  are  constantly- 
feeding.  The  exudations  from  such  sores  are  teeming  with  Leish- 
man  bodies,  Leishmania  tropica  (Fig.  15A  and  B),  which  very 
closely  resemble  those  of  kala-azar.  In  some  cities  infection  by 
these  parasites  is  so  com- 
mon and  so  inevitable 
that  normal  children  are 
expected  to  have  the  dis- 
ease and  visitors  to  the 
cities  seldom  escape  a 
sore  as  a  souvenir,  even 
if  present  for  only  a  short 
time.  In  Bagdad,  Wenyon 
has  shown  that  almost  as 
soon  as  the  children  are 
relieved  of  the  wrappings 
in  which  they  are  covered 
as  babies,  and  allowed  to 
run  free  and  play  in  the 
streets,  they  are  almost 
certain  of  infection.  Since 
one  attack  gives  immu- 
nity,    oriental     sores     ap-        Fig.  15.    Parasites  of  oriental  sore  (Lm/imanMi 

pearing  on  an  adult  person    [''''^''^^ '  /^'  ^^  ^J"^  ^'  parasites  from  sore,  the 
.  1     1  .  torpedo-shaped  forms  (A)   being  found  outside 

m  Bagdad  brands  him  as    the  cells,  the  others  (B  and  C)  within  the  cells; 
a     new     arrival,     and     the    D    Herpetomonas   form   taken  from  bedbug  48 

hours  after  feeding  on  sore;  E,  the  same,  dividing 
same  is  undoubtedly  true    form.      X  4000.     (After  Wenyon.) 

in    many    other    tropical 

cities.  The  disease  is  prevalent  from  India  through  Persia,  Syria 
and  Arabia  and  along  the  south  shore  of  the  Mediterranean  as 
far  as  Morocco.  True  oriental  sore  probably  occurs  commonly 
in  many  cities  of  tropical  South  America,  though  here  it  is  ob- 
viously difficult  to  distinguish  it  from  the  skin  sores  of  espundia. 
Transmission.  —  Though  oriental  sores  may  appear  at  any  time 
of  the  year,  they  are  particularly  abundant  in  the  autumn  months 
in  most  cities  of  the  Old  World.  Since  the  usual  time  of  the 
appearance  of  the  sore,  as  nearly  as  can  be  judged,  is  about  two 
months  after  infection,  though  sometimes  much  less  and  often 
much  longer  than  this,  infection  must  usually  occur  during  the 
hot  mid-summer  months.     This  fact  suggests  the  probability  of 


86  LEISHMAN  BODIES  AND  LEISHMANIASIS 

the  parasites  being  transmitted  by  some  biting  insect  which 
appears  during  this  season.  There  can  be  no  doubt  that  the 
myriads  of  flies  which  collect  on  the  sores  must  mechanically 
carry  the  parasites  in  many  cases  from  infected  individuals  and 
deposit  them  on  wounds  or  cuts  of  others  where  they  gain  access 
to  the  body.  It  may  be  that  one  or  more  kinds  of  insects  act  as 
intermediate  hosts;  in  fact,  it  has  been  claimed  that  in  India  the 
bedbug  is  an  intermediate  host  for  this  as  well  as  for  the  kala-azar 
parasite.  In  Teheran,  where  a  large  proportion  of  the  dogs  (in 
one  case  15  out  of  21  street  dogs)  show  Leishmanian  sores,  the 
parasites  have  been  found  in  the  gut  of  a  fly,  Hippohosca  canina, 
common  on  the  dogs.  Camels  and  horses  are  also  subject  to 
infection  in  some  places.  A  number  of  French  workers  in  North 
Africa  have  suggested  that  the  sandfly,  Phlehotomus  minutus, 
which  is  very  abundant  there,  is  the  transmitter  of  the  disease 
and  that  the  common  Algerian  gecko,  Tarentola  mauritanica, 
may  play  the  role  of  a  reservoir  for  the  disease.  The  sandflies 
swarm  about  the  lizards  in  large  numbers,  and  also  bite  man 
readily.  Leishman  bodies  have  been  found  in  the  blood  of  a 
number  of  geckos  near  Tunis.  On  the  western  face  of  the  Andes 
in  Peru  there  occurs  a  similar  disease  known  as  uta,  which  has  been 
shown  by  Townsend,  of  the  U.  S.  Bureau  of  Entomology,  to 
develop  in  the  intestine  of  two  little  gnats,  Forcipomyia  utce  and 
Fordpomyia  townsendi,  very  closely  allied  to  the  American 
"  punkies."  Inoculation  of  the  gut  contents  of  these  insects  into 
guinea-pigs  produces  sores  believed  to  be  identical  with  uta,  and 
Townsend  believes  the  insects  transmit  the  disease  in  nature  by 
voiding  the  Leishman  bodies  from  the  anus  while  sucking  blood, 
the  puncture  being  contaminated  in  this  way.  Whether  this  dis- 
ease is  a  very  mild  form  of  espundia,  described  below,  or  is  more 
closely  allied  to  true  oriental  sore,  is  difficult  to  say.  According 
to  the  description  given  by  Dr.  Strong  and  his  colleagues  of  the 
Harvard  expedition  to  Peru,  uta  is  not  so  mild,  and  may  attack 
the  mucous  membranes  as  does  espundia.  Possibly  both  diseases 
occur  there.  Dr.  Strong  has  pointed  out  that  the  flagellated 
stage  of  the  uta  parasite  differs  from  that  of  other  Leishmania 
in  possessing  a  basal  granule  in  addition  to  the  nucleus  and  para- 
basal body. 

The  Disease.  —  Although  oriental  sore  often  has  a  long  incu- 
bation period,  and  produces  such  profound  constitutional  changes 


COURSE  OF  ORIENTAL  SORE  87 

as  to  build  up  an  immunity  which  is  usually  effective  for  life, 
the  general  symptoms  are  so  mild  as  to  be  usually  unnoticed. 
Slight  fevers  and  general  malaise  are  frequent  at  all  times  in 
tropical  countries,  and  it  would  be  extremely  difficult  to  connect 
such  non-characteristic  symptoms  with  a  sore  appearing  perhaps 
months  afterward.  There  is  some  evidence,  however,  that  at 
least  in  some  cases  fevers  do  occur  which  are  attributable  to  the 
parasites  of  oriental  sore. 

The  nature  and  course  of  the  sores  vary  to  some  extent  in 
different  locaUties.  The  sore  usually  begins  as  a  small  dark  pimple 
which  causes  very  slight  itching  and  little  if  any  inflammation  of 
the  surrounding  skin.  The  pimple  grows  slowly  and  develops  in 
one  of  two  ways,  forming  either  an  ulcerating  or  a  non-ulcerating 
sore,  more  popularly  known  as  female  and  male  sores  respectively. 
In  the  former  type,  under  a  flaky  scab  which  soon  falls  away  or  is 
scratched  off,  there  develops  a  shallow  ulcer  exuding  a  foul-smell- 
ing yellow  fluid.  Usually  the  sore  covers  an  area  about  the  size 
of  a  dollar,  the  older  portion  often  healing  while  the  ulcer  is  still 
extending  in  another  direction.  The  surface  of  the  ulcer  is 
covered  by  red  granulations  which  bleed  readily.  In  most  lo- 
calities these  ulcers  are  not  painful,  but  those  occurring  along 
the  eastern  slope  of  the  Andes  in  Peru  and  Bolivia  are  said  to  be 
very  painful. 

The  non-ulcerating  or  male  sores  grow  slowly  and  develop  a 
covering  of  white  flaky  scales  over  a  thin  red  skin,  below  which  is 
a  mass  of  red  granulations  where  the  parasites  may  be  found  in 
large  numbers.  The  non-ulcerating  sores  sometimes  break  down 
and  ulcerate,  but  usually  grow  to  about  the  same  size  as  do  the 
"  female  "  sores,  and  then  gradually  shrink,  finally  healing  as 
do  the  others. 

The  sores,  of  either  kind,  nearly  always  occur  on  exposed  parts 
of  the  body,  as  the  face,  neck,  arms  or  legs.  Occasionally  they 
occur  on  the  lips  or  edges  of  the  nose  and  spread  to  the  mucous 
membranes,  but  this  must  not  be  confused  with  the  mucous 
membrane  ulcerations  of  American  leishmaniasis.  A  single  sore 
is  the  most  common  condition,  but  secondary  sores  sometimes 
develop  in  its  vicinity,  and  sometimes  a  great  many  sores  may 
occur  on  an  individual.  In  the  Peruvian  uta  several  sores  seem 
to  be  the  rule,  these  occurring  at  the  sites  of  the  bites  of  gnats 
and  possibly  other  insects. 


88  LEISHMAN  BODIES  AND  LEISHMANIASIS 

The  sores  usually  last  for  a  year,  more  or  less,  gradually  healing 
over,  but  leaving  permanent  scars.  The  uta  sores  of  the  Peru- 
vian Andes,  which  have  a  much  shorter  incubation  period,  may 
run  their  course  and  heal  in  much  less  time,  according  to  Town- 
send  in  as  short  a  time  as  15  days.  Except  in  rare  cases,  after 
an  oriental  sore  has  once  run  its  course  and  healed  a  person  is 
permanently  immune  to  any  further  attacks. 

Treatment  and  Prevention.  —  The  use  of  tartar  emetic  as  a 
cure  for  oriental  sores  is  as  productive  of  good  results  as  it  is  in 
the  case  of  other  Leishmanian  infections.  With  the  usual  one  per 
cent  or  two  per  cent  solutions  of  this  drug  injected  into  the  veins 
the  sores  yield  promptly  and,  if  treated  at  an  early  stage,  can  be 
prevented  from  leaving  scars. 

In  badly  infected  places  there  might  be  some  advantage  in 
allowing  the  sore  to  run  its  course,  inoculating  it  on  an  inexposed 
part  of  the  body  where  it  could  cause  no  visible  disfigurement, 
since  in  this  way  a  permanent  immunity  to  further  infection 
could  be  prevented.  It  is  better  to  keep  the  sores  open  than  to 
allow  a  scab  to  form  over  them,  since  the  scab  shuts  in  the  pus 
and  results  in  more  extensive  ulceration  and  inflammation.  Ap- 
plications of  various  kinds  which  will  soothe  the  inflammation 
and  keep  the  sores  as  dry  and  clean  as  possible  are  beneficial. 
The  use  of  hypodermic  injections  of  dead  cultures  of  the  parasite, 
as  in  anti-typhoid  vaccinations,  has  been  found  to  hasten  the 
healing.  The  inoculation  of  the  active  disease  germs  on  inex- 
posed parts  of  the  body,  especially  in  young  children  in  whom 
the  sores  are  never  very  extensive,  is  easily  accomplished,  and  has 
been  practiced  in  Bagdad  and  other  cities  where  the  disease  is  so 
prevalent  as  to  make  avoidance  of  it  almost  impossible.  Such 
a  procedure  tends  to  lessen  the  number  of  exposed  sores,  to 
which  flies  or  other  insects  might  get  access.  Unless  the  disease 
should  be  found  to  be  transmitted  by  insects  which  suck  the 
parasites  from  the  circulating  blood,  which  seems  very  unhkely, 
the  protection  of  the  sores  will  greatly  reduce  the  prevalence  of 
this  unpleasant  feature  of  tropical  cities. 

It  is  possible  that  an  immunity  may  be  established  by  the 
inoculation  of  dead  parasites  as  in  the  case  of  typhoid  fever,  but 
this  has  not  yet  been  demonstrated. 


SKIN  SORES  OF  ESPUNDIA  89 

Espundia  or  American  Leishmaniasis 

In  many  parts  of  Brazil,  Paraguay,  Bolivia,  Venezuela,  French 
Guiana  and  other  countries  of  tropical  South  America  there 
occurs  a  horrible  form  of  Leishmanian  ulcers  which  attack  both 
the  skin  and  the  mucous  membranes  of  the  nose  and  mouth 
cavity.  These  ulcers  do  not  grow  to  a  limited  size  and  then  heal, 
but  slowly  and  constantly  spread  further  and  further,  lasting 
for  a  period  of  five,  ten,  fifteen  or  more  years.  The  disease  goes 
by  a  great  variety  of  local  names  of  which  espundia  is  the  most 
common.  The  best  name  of  all  is  probably  ''  American  Leish- 
maniasis." The  name  *'  buba  braziUensis  "  has  been  given  it  by 
some  writers,  but  erroneously,  since  this  name  properly  belongs 
to  another  tropical  disease,  yaws.  A  few  cases  of  Leishmania 
ulcers  have  been  observed  in  dogs  in  South  America.  Monkeys 
can  be  experimentally  inoculated.  The  organism  causing  these 
intractable  ulcers  has  been  named  Leishmania  americana  (bra- 
ziUensis). It  is  a  very  minute  animal,  and  is  found  usually  in 
rather  scanty  numbers  in  the  sores;  it  can  be  distinguished 
from  the  parasite  of  oriental  sore,  L.  tropica,  of  which  many 
authors  believe  it  is  a  mere  variety,  rather  by  its  pathogenic  effects 
than  by  any  pecuHarity  of  form.  Flagellated  forms  of  the  para- 
site are  occasionally  found  in  the  sores. 

Skin  Sores.  —  The  sores  on  the  skin,  which  do  not  always 
ulcerate,  usually  begin  as  one  or  two  itching  spots  that  seem  to 
be  produced  by  the  bites  of  insects.  If  the  sores  are  of  the  non- 
ulcerating  type  there  is  produced  a  great  deal  of  red  granular 
tissue,  raised  slightly  above  the  surrounding  skin,  and  bleeding 
easily.  The  surface,  which  is  rosy  in  color,  is  rough,  resembling, 
according  to  one  author,  a  cauliflower.  An  intolerably  foul- 
smelling  fluid  is  constantly  emitted  which  sometimes  dries  over 
the  sore  to  form  a  crust  of  varying  thickness.  The  fluid  given 
off  is  infectious  and  starts  new  sores  if  it  comes  in  contact  with 
any  broken  skin  on  the  same  or  another  individual. 

In  the  ulcerating  type  of  the  disease  in  the  skin  the  same  fetid 
fluid  is  emitted,  but  instead  of  the  sore  being  elevated,  it  is  ex- 
tensively excavated  and  has  raised  borders.  Often  an  enclosing 
crust  forms  over  it  and  it  is  improperly  called  a  "  dry  sore."  In 
this  case  the  fluid  is  shut  in  between  the  crust  and  the  sore  and 
causes  even  more  intensive  destruction  of  the  tissues.     Some- 


90  LEISHMAN  BODIES  AND  LEISHMANIASIS 

times  nearby  lymph  glands  also  become  infected.  Such  general 
symptoms  as  evening  fever,  pains  in  the  joints,  headache,  etc., 
sometimes  accompany  the  ulceration,  probably  due  to  the  ab- 
sorption of  toxins. 

As  remarked  before,  the  exudations  from  the  sores  are  extremely 
infectious  for  either  the  same  individual  or  another  one.  Con- 
sequently it  is  not  infrequent  to  find  on  a  single  individual  a 
great  many  sores,  up  to  50  or  more,  in  all  stages  of  development, 
though  more  often  there  are  only  a  few.  In  one  case  recorded 
from  Brazil  there  were  35  active  sores  and  29  extinct  ones,  and 
these  were  arranged  in  a  more  or  less  symmetrical  manner,  sug- 
gesting the  influence  of  the  nervous  system  on  their  location. 
The  sores  become  secondarily  infected  with  bacteria  and  spiro- 
chsetes  and  are  sometimes  attacked  by  screw-worms  and  other 
fly  maggots.  The  rarity  of  Leishman  bodies  in  the  late  stages  of 
the  sores  suggests  that  the  secondary  infections  may  then  play 
an  important  role,  though  the  prompt  cure  which  follows  treat- 
ment destructive  to  the  protozoans  shows  that  the  latter  still  play 
a  leading  part. 

Mucous  Membrane  Ulceration.  —  A  far  more  vicious  mani- 
festation of  the  disease  and  one  which  follows  the  cutaneous  sores 
is  the  ulceration  of  the  mucous  membranes  of  the  nose  and  mouth 
(Fig.  16).  It  may  be  several  months  or  over  a  year  after  the 
skin  sores  develop  and  often  after  they  have  healed  that  the 
mucous  ulcerations  appear.  In  rare  cases  ulcers  have  been 
known  to  occur  in  the  vagina  also.  Ordinarily  the  infection 
commences  as  a  tiny  itching  hardness  or  swelling  of  the  mucous 
membrane,  usually  in  the  nose,  the  infected  membrane  becoming 
inflamed,  and  marked  either  with  small  granular  sores  or  with 
bhster-like  swellings.  The  lymph  glands  in  the  infected  regions 
become  swollen  and  turgid.  A  granular  ulceration  begins  in  a 
short  time,  invading  all  the  mucous  membranes  of  the  nose  and 
spreading,  by  means  of  infective  fluid  which  flows  down  over  the 
upper  lip,  into  the  mouth  cavity,  attacking  the  membranes  of 
the  hard  and  soft  palate.  Its  advance  is  obstinate  and  slow,  and 
gives  rise  to  serious  complications.  The  nostrils  become  too 
clogged  to  admit  the  passage  of  sufficient  air  and  the  patient 
has  to  keep  his  mouth  constantly  open  to  breathe.  His  repul- 
sive appearance  and  fetid  breath  help  to  make  his  life  miserable. 
Affections  of  the  organs  of  smell  and  hearing,  and  even  sight, 


TREATMENT  OF  ESPUNDIA 


91 


often  supervene,  and  the  voice  is  weakened  or  even  temporarily 
lost.  The  digestive  tract  becomes  upset  from  the  constant  escape 
down  the  throat  of  the  exudations  from  the  ulceration,  mixed  with 
saliva  or  food.  A  spreading  of  the  nose  due  to  the  eating  away 
of  the  septum  is  a  characteristic  feature.  Although  in  late  stages 
of  the  disease  the  entire  surface  of  the  palate  and  nasal  cavities 
is  attacked,  and  the  septum  between  the  nostrils  destroyed,  the 
bones  are  left  intact,  a  feature  which  readily  distinguishes  a 
Leishmanian  ulcer  from  a  syphilitic  one.  Usually  the  victim  of 
espundia,  after  long  suffering,  sometimes  for  20  or  30  years, 
succumbs  to  the  disease  from  pure  exhaustion  and  from  poison- 
ing by  exuded  liquids  which  are  swallowed. 


Fig.  16.     A  case  of  espundia  before  and  after  treatment  with  tartar  emetic. 
(After  d'Utra  e  Silva.) 

Treatment  and  Prevention.  —  It  was  in  connection  with  ulcers 
caused  by  Leishmania  americana  that  the  curative  action  of 
tartar  emetic  was  first  worked  out  by  Vianna  in  the  Institute 
Oswaldo  Cruz  at  Rio  de  Janeiro.  The  treatment  of  espundia 
with  this  drug,  injected  into  the  veins,  has  been  thoroughly  tried 
out  in  the  past  two  years  with  great  success.  Although  the 
mucous  membrane  ulcers  do  not  yield  to  the  treatment  as  readily 
as  do  skin  sores,  yet  they  can  be  cured  with  persistent  treatment, 
even  in  cases  in  which  the  nose  and  throat  had  been  infected  for 
several  years.  The  tartar  emetic  is  injected  as  a  one  to  two  per 
cent  solutian,  as  for  other  Leishmanian  diseases,  five  to  ten  cc. 


92  LEISHMAN   BODIES  AND  LEISHMANIASIS 

being  injected  daily  for  from  five  to  40  days.  As  remarked  else- 
where, it  must  be  administered  very  carefully  and  slowly  since 
it  is  likely  to  produce  much  irritation. 

Practically  nothing  can  be  said  about  the  prevention  of  the 
disease,  since  its  method  of  transmission  is  unknown.  The 
natives  of  South  America  believe  that  it  results  from  the  bite  of 
some  jungle  insect,  probably  a  horsefly  (tabanid),  but  nothing 
definite  is  known  about  it.  Blackflies,  mosquitoes  and  ticks 
have  been  suggested  as  transmitters  also.  Since  the  disease  is 
contracted  in  forests  in  the  daytime,  and  the  sores  usually  de- 
velop on  exposed  parts  of  the  body,  tabanids  seem  to  be  in- 
criminated by  circumstantial  evidence.  However,  it  is  possible 
that  houseflies  or  other  non-biting  insects  may  carry  the  infection, 
the  punctures  of  biting  insects  serving  merely  to  open  a  door  of 
entrance  for  the  parasites.  Natives  of  Paraguay  believe  that 
rattlesnakes  harbor  the  parasites  and  that  the  latter  are  trans- 
mitted to  man  either  by  blackflies  or  ticks,  both  of  which  attack 
the  snakes.  Although  only  a  popular  belief,  this  is  interesting  in 
view  of  the  incrimination  of  geckos  as  reservoirs  of  oriental  sore 
parasites  in  Algeria. 

It  would  seem  obvious  that  in  case  a  skin  sore  of  the  espundia 
type  develops,  great  care  should  be  taken  not  to  allow  the  mu- 
cous membranes  to  become  infected  by  contact.  Yet  a  case  is 
cited  by  da  Matta  where  an  ignorant  wood-cutter  who  had  been 
tormented  by  espundia  of  the  skin  for  five  years  and  who  persist- 
ently cleaned  his  nose  with  infected  fingers,  never  developed  the 
slightest  affection  of  the  mucous  membranes.  In  other  cases, 
simultaneous  affection  of  the  mucous  membranes  and  skin  is 
common. 


CHAPTER  VT 
TRYPANOSOMES  AND   SLEEPING   SICKNESS 

Importance  of  Trypanosome  Diseases.  —  One  of  the  blackest 
clouds  overhanging  the  civiUzation  of  tropical  Africa  is  the 
terrible  scourge  of  sleeping  sickness,  a  disease  caused  by  protozoan 
parasites  known  as  trypanosomes.  The  destiny  of  the  equatorial 
parts  of  Africa  depends  largely  on  the  issue  of  the  struggle  of 
medical  science  against  this  haunting  malady.  The  ravages  of 
the  disease  were  well  known  to  the  old  slave  traders,  and  the 
presence  of  "  lazy  niggers "  lying  prostrate  on  wharves  and 
decks  with  saliva  drooling  from  their  mouths,  insensible  to  emo- 
tions or  pain,  was  a  famiUar  sight.  It  did  not  take  these  astute 
merchants  long  to  find  that  death  was  the  inevitable  outcome  of 
the  disease,  and  they  very  soon  recognized  swollen  glands  in  the 
neck  as  an  early  symptom  and  refused  to  accept  as  slaves  negroes 
with  swollen  glands  (see  Fig.  24).  Nevertheless  sleeping  sick- 
ness must  often  have  been  introduced  with  its  parasites  into 
various  parts  of  North  and  South  America,  as  it  frequently  is  even 
at  the  present  time,  and  only  the  absence  gf  a  suitable  means  of 
transmission  has  saved  the  Western  Hemisphere  from  being 
swept  by  it. 

Up  to  about  thirty  years  ago  sleeping  sickness  was  confined  to 
a  hmited  part  of  tropical  West  Africa,  but  with  the  opening  up  of 
Central  Africa  by  whites  and  the  consequent  movements  of 
disease-carrying  inhabitants  to  new  portions  of  the  continent, 
the  afflicted  country  was  greatly  extended.  The  great  explorer 
Stanley,  in  his  expedition  to  reach  Emin  Pasha,  was  almost  un- 
questionably responsible  for  the  introduction  of  the  scourge  into 
Uganda  and  the  lake  regions  of  Central  Africa  in  1888,  where  it 
had  hitherto  been  unknown.  In  one  district  of  Central  Africa 
the  population  was  reduced  from  300,000  to  100,000  in  the  course 
of  seven  years,  from  1901  to  1908,  and  there  are  records  of  whole 
villages  and  islands  being  depopulated. 

In  1909  there  occurred  a  case  of  sleeping  sickness  contracted  in 

93 


94 


TRYPANOSOMES  AND  SLEEPING  SICKNESS 


Rhodesia  in  southeastern  Africa  occasioned  by  a  distinct  and  ap- 
parently newly  originated  type  of  trypanosome,  as  indicated 
by  its  sudden  appearance  and  startlingly  rapid  spread.  This 
type  of  sleeping  sickness  is  more  deadly  than  the  older  type  and 
there  is  reason  to  fear  that  unless  efficient  methods  of  control- 
ling it  and  stamping  it  out  are  discovered  it  will  spread  over  a 
large  part  of  tropical  Africa.  The  disease  has 'already  spread 
over  a  great  part  of  Rhodesia,  Nyasaland  and  Portugese  East 
Africa,  and  has  been  reported  from  German  East  Africa.  There 
is  apparently  a  rather  high  natural  immunity  to  the  disease,  which 
alone  is  responsible  for  the  small  number  of  the  victims. 

In  the  same  year,  1909,  a  fever 
caused  by  a  trypanosome  was  dis- 
covered by  Chagas  in  tropical 
Brazil,  and  has  since  been  found 
to  be  widely  distributed  there,  and 
to  be  the  cause  of  much  of  the 
non-malarial  "  fever  "  for  which 
the  jungles  of  tropical  South 
America  are  famous. 

The  Parasites.  —  The  trypano- 
somes,  next  only  to  the  malarial 
parasites,  may  be  considered  man's 
most  deadly  enemies  among  the 
Protozoa.  Like  the  Leishman 
bodies  described  in  the  preceding 
chapter,  they  are  members  of  a 
primitive  group  of  the  class  Flagel- 
lata,  but  of  somewhat  higher  or- 
ganization, and  probably  higher  in 
the  scale  of  evolution.  Trypano- 
somes  are  very  active,  wriggling 
little  creatures  somewhat  suggest- 
ing diminutive  "  artistic  dolphins  "  (Fig.  17).  They  are  about  25  /j, 
(about  YXHTTT  of  an  inch)  or  even  less  in  length,  spindle-shaped,  and 
somewhat  flattened  from  side  to  side  like  an  eel.  Along  the  "  back" 
runs  a  flagellum  connected  with  the  body  by  an  undulating  mem- 
brane, Hke  a  long  fin  or  crest.  This  terminates  at  what  is  really 
the  anterior  end  in  a  free  tail-like  flagellum.  It  is  by  means  of 
the  wave  motions  of  the  membrane  and  the  lashing  of  the  flagel- 


FiG.  17.  Trypanosoma  gamhiense, 
slender  form.  p.  b.,  parabasal  body; 
b.  gr.,  basal  granule;  und.  m.,  undu- 
lating membrane;  n.,  nucleus;  fl.,  fla- 
gellum.     X4000. 


DEVELOPMENTAL  STAGES 


95 


lum  that  the  animal  moves  through  the  blood  or  other  fluids  of 
the  body,  either  forward  or  backwards,  so  rapidly  that  it  is  difficult 
to  observe  under  the  high  power  of  a  microscope  as  it  wends  its 
way  between  the  blood  corpuscles  on  a  shde.  The  body  of  the 
animal  contains,  in  addition  to  the  large  round  nucleus  near  the 
fniddle,  another  deeply-staining  structure,  the  parabasal  body 
(see  p.  31)  at  the  posterior  end  near  where  the  flagellum  origi- 
nates.    The  body  also  contains  other  granules  of  various  sizes. 

There  are  a  great  many  kinds  of  trypanosomes  inhabiting  many 
different  animals.  Those  living  in  cold-blooded  animals  have 
no  apparent  effect  on  their  hosts  but  the  species  infesting  mammals 
almost  always  cause  disease.  In  man  their  effect  is  particularly 
deadly  and  the  African  species  usually  cause  death  if  allowed  to 
run  to  the  sleeping  sickness  stage.  Unlike  many  kinds  of  para- 
sites most  trypanosomes  can  live  in  a  great  many  different  hosts. 
The  common  sleeping  sickness  trypanosome,  for  instance,  can 
live  not  only  in  man  but  also  in  monkeys,  dogs,  rodents,  domestic 
animals  and  a  large  number  of  the  wild  game  animals  of  Africa. 

Most  kinds  of  trypanosomes,  like  the  malarial  parasites,  live 
only  part  of  their  life  histories  in  the  blood  or  other  fluids  of 
their  vertebrate  hosts,  undergo- 
ing another  phase  of  it  in  the 
digestive  tracts  of  insects  or  other 
invertebrates.  In  their  interme- 
diate hosts  they  undergo  remark- 
able transformations;  the  whole 
series  of  forms  through  which 
trypanosomes  may  pass  in  their 
development,  and  which  may 
represent  a  phylogenetic  as  well 
as  an  ontogenetic  series,  is  shown 
in  Fig.  18.     The  first  or  Leish- 

.     -                r  •   1.     X       J       J.  J.T-  Fig.   18.     Diagram  of  developmental 

mama  form,  which  stands  at  the  types  of  trypanosomes;  A,  trypanosome 

foot   of   the   series,    is   a   rounded  form;  B,  Cnthidial  form;  C,  Herpeto- 

,       ,           .,,           ,                      ,1  monas form ; D,  Leishmania form.  (After 

body  With   a  large   central   nu-  wenyon.) 
cleus  and  small  rod-shaped  para- 
basal body  usually  set  at  a  tangent  to  the  nucleus  (Fig.  18D). 
Next  in  development  comes  the  Herpetomonas  form  which  differs 
in  having  a  long  slender  body  and  in  having  a  flagellum  produced 
from  the  parabasal  body  (Fig.  18C).     Next  comes  the  Crithidia 


96  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

form,  differing  from  the  preceding  in  that  the  parabasal  body 
has  moved  back  to  near  the  middle  of  the  body,  and  the  flagellum 
is  connected  with  the  body  for  half  its  length  by  an  undulating 
membrane  (Fig.  18B).  This  type  is  a  very  common  develop- 
mental phase  in  nearly  all  trypanosomes,  but  it  is  also  the  adult 
condition  of  many  insect  parasites.  Finally  there  occurs  the 
fully-developed  trypanosome  form  (Fig.  18A),  apparently  es- 
pecially adapted  in  form  and  structure  for  life  in  vertebrate 

bodies.  The  method  of  develop- 
ment of  this  form  from  a  crithidial 
type  can  easily  be  seen  from  Fig.  18. 
Only  the  first  or  Leishmania  form 
and  the  last  or  trypanosome  form 
normally  occur  in  vertebrate  bodies, 
though  all  of  the  four  types  are 
found  in  the  digestive  tracts  of  in- 
vertebrates. The  fact  that  some 
flagellates  never  develop  further 
than  the  Herpetomonas  form,  and 
others  never  further  than  the  Crith- 
idia  form,  makes  a  study  of  this 
group  of  Flagellates  very  confusing, 
since  when  a  Herpetomonas  or  crith- 
idial type  is  found  in  an  insect  gut 
it  is  very  difficult  if  not  impossible 
Fig.  19.  Trypanosoma  rhodesi-  ^o  Say  whether  it  is  an  adult  animal 
ense,  from  blood  of  monkey  inocu-  which  never  Undergoes  any  further 

lated  from  case  of  human  sleeping    j        i  ^  •  i  j        i 

sickness.  Note  posterior  position  of  development  or  IS  only  a  develop- 
nucieus  in  short  blunt  forms,  espe-  mental  phase  of  a  trypanosome  of 

cially    in    lower    figure.        X  2000.  i.   u      i.  •        i 

(After  Kinghorn  and  Yorke.)  ^  vertebrate  animal. 

It  is  often  very  difficult  to  dis- 
tinguish different  species  of  trypanosomes;  of  over  70  known 
species  only  a  few  can  be  distinguished  on  morphological  grounds. 
Average  size,  position  of  nucleus  and  parabasal  body,  length  of 
snout,  and  presence  or  absence  of  a  free  flagellum  are  sometimes 
useful  in  identifjdng  them.  More  reliable,  however,  are  their  so- 
called  "  biological  characteristics,"  such  as  pathologic  effects  on 
different  animals,  susceptibility  of  different  hosts,  the  effect  of 
serum  immune  to  certain  species,  and  the  "  cross-immunity  re- 
actions."    The  last  is  the  most  certain  method.     Thus,  if  an 


PATHOGENIC  SPECIES 


97 


animal  has  recovered  from  an  attack  by  one  strain  of  trypano- 
some  it  is  rendered  immune  and  will  not  succumb  to  second 
attacks  of  the  same  strain,  though  it  is  still  susceptible  to  others. 
As  remarked  before  there  are  at  least  three  species  of  trypano- 
somes  which  are  known  to  cause  disease  in  man,  two  in  Africa 
and  one  in  South  America.  The  African  species,  causing  sleep- 
ing sickness,  are  the  most  deadly  but  the  South  American  species 
is  frequently  fatal,  especially  to  children,  and  often  renders  a  life 
worse  than  useless.     The  Gambian  trypanosome,   Trypanosoma 


Fig.  20.  Trypanosoma  gambiense  in  rat  blood,  showing  long,  intermediate  and 
short  forms  all  in  one  microscopic  field.  X  about  1200.  Drawn  from  microphoto- 
graph  by  Minchin. 


gambiense,  is  the  cause  of  the  commoner  and  more  widespread 
form  of  sleeping  sickness,  while  the  Rhodesian  species,  T.  rho- 
desiense,  is  the  cause  of  the  recently  established  East  African 
form  of  the  disease.  The  most  salient  distinguishing  character- 
istic between  these  two  species  of  trypanosomes  is  the  posterior 
situation  of  the  nucleus  of  the  Rhodesian  parasite  in  a  certain 
per  cent  of  individuals  when  they  are  developed  in  rats  and  some 
other  animals  (Fig.  19).  This  is  a  feature  never  observed  in  the 
Gambian  trypanosome.     Both  species  vary  a  great  deal  in  form, 


98  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

and  three  distinct  types  may  be  observed  at  once  in  the  blood  of 
an  infected  animal,  a  long  slender  form  with  a  long  free  flagellum, 
a  short  stumpy  form  with  a  short  flagellum  and  a  form  interme- 
diate between  these  (Fig.  20).  Some  investigators  regard  the 
trypanosome  causing  the  mild  sleeping  sickness  of  Nigeria  as  a 
distinct  species,  named  T.  nigeriense. 


Sleeping  Sickness 

Transmission.  —  Sleeping  sickness  of  either  type,  and  also 
many  trypanosome  diseases  of  lower  animals,  is  transmitted 
primarily  by  certain  species  of  tsetse  flies  which  act  as  inter- 
mediate hosts  for  the  trypanosomes.  The  Gambian  parasite,  as 
first  shown  by  Sir  David  Bruce,  is  normally  transmitted  by  the 
tsetse  fly,  Glossina  palpalis,  and  its  distribution  is  now  almost 
coincident  with  the  range  of  this  species.  It  occurs  on  the 
west  coast  of  Africa  from  the  Senegal  River  to  the  State  of 
Mossamedes  in  Portuguese  West  Africa,  including  nearly  all 
the  tributaries  of  the  Niger  and  Congo  Rivers.  Eastward  it 
extends  to  the  valley  of  the  Upper  Nile  and  Lake  Victoria  Nyanza 
in  Uganda  and  along  the  east  shore  of  Lake  Tanganyika. 

The  Rhodesian  trypanosome  depends  on  the  more  widespread 
and  less  easily  controlled  Glossina  morsitans.  This  species  of 
tsetse  fly  occurs  all  the  way  from  northeastern  Transvaal  to 
northern  Nigeria  in  West  Africa  and  to  southern  Sudan  in  the 
basin  of  the  Nile  in  East  Africa.  So  far,  the  disease  caused  by 
the  Rhodesian  parasite  is  limited  to  a  small  portion  of  East 
Central  Africa  but  it  is  spreading  both  north  and  south. 

Experimentally  other  species  of  tsetses  are  able  to  transmit 
the  Gambian  disease,  but  it  is  doubtful  whether  any  except 
G.  palpalis  are  important  transmitting  insects  in  nature.  As  in- 
timated above  it  is  only  the  absence  of  tsetse  flies  in  other  parts 
of  the  world  that  we  have  to  thank  for  the  fact  that  sleeping 
sickness  when  introduced  is  not  propagated.  Experiments  show 
that  it  is  also  possible  for  the  Gambian  trypanosome  to  be  trans- 
mitted mechanically  by  the  stable-flies,  Stomoxys,  though  this 
probably  seldom  happens  in  nature.  Macfie  has  shown  that  in 
Nigeria  the  human  trypanosomes  undergo  developmental  stages 
in  a  stable-fly,  S.  nigra,  but  circumstances  did  not  allow  him  to 
determine  whether  the  salivary  glands  become  infective  as  in 


DEVELOPMENT  IN  TSETSE  FLY  99 

tsetse  flies.  There  is  evidence  that  sleeping  sickness,  Uke  surra, 
a  trypanosome  disease  of  horses,  may  also  be  transmitted  sexu- 
ally or  through  abrasions  of  the  skin,  but  this  is  certainly  not 
the  usual  method  of  transmission. 

The  tsetses  are  blood-sucking  flies  resembhng  stable-flies, 
which  inhabit  the  brushy  borders  of  lakes,  streams  or  swamps, 
—  the  so-called  "fly-belts."  The  distinguishing  characteristics 
of  the  tsetse  flies  and  of  the  various  disease-carrying  species  are 
discussed  in  the  chapter  on  biting  flies,  p.  490. 

For  a  long  time  it  was  thought  that  the  tsetse  flies  could  trans- 
mit trypanosomes  only  in  a  simple  mechanical  way,  the  para- 
sites adhering  to  the  proboscis,  and  being  subsequently  injected 
into  the  blood  of  another  person.  It  is  now  known  that  the 
trypanosomes  of  sleeping  sickness  can  be  transferred  in  this 
manner  only  for  a  few  minutes  after  an  infective  feed,  but  that  the 
fly  again  becomes  infective  after  a  period  of  three  or  four  weeks. 
Meanwhile  the  parasites  have  undergone  a  series  of  changes  in 
the  gut  of  the  insect  and  finally  become  stored  in  the  salivary 
glands  from  which  they  are  poured  with  the  saUvary  juices  into 
the  blood  of  a  new  victim. 

Life  Cycle  in  Fly. — According  to  observations  on  Trypanosoma 
gamhiense  in  Glossina  palpalis  by  Miss  Robertson  the  critical 
time  for  the  trypanosomes  after  they  are  sucked  up  by  the  fly 
is  when  the  fly  feeds  the  next  time,  since  in  many  cases  they  are 
swept  out  of  the  body  with  the  new  influx  of  blood,  or  digested. 
Having  stood  their  ground  until  they  have  become  established  in 
the  new  influx  of  blood  they  multiply  so  rapidly  that  permanent 
infection  of  the  fly  is  almost  certain.  The  difficulty  experienced 
by  the  parasites  in  estabUshing  themselves  in  the  gut  of  their 
insect  hosts  largely  accounts  for  the  relatively  low  percentage 
(usually  less  than  five  per  cent)  of  infections  which  result  from^feed- 
ing  of  tsetse  flies  on  infected  blood.  When  conditions  are  favor- 
able for  development  in  the  fly  the  parasites  multiply  first  in 
the  middle  intestine,  producing  long-snouted  forms  such  as  shown 
in  Fig.  2 IB.  After  the  tenth  to  fifteenth  day  long  slender  forms 
(Fig.  21C)  are  developed,  and  these  move  forward  in  the  digestive 
tract.  These  slender  trypanosomes  have  long  snouts  and  differ 
most  strikingly  from  the  earUer  forms  in  the  appearance  of  the 
nucleus  (Fig.  21C).  After  several  days  more  the  trypanosomes 
make  their  way  to  the  fly's  salivary  glands,  to  the  walls  of  which 


100 


TRYPANOSOMES  AND  SLEEPING  SICKNESS 


they  attach  themselves  "by  their  flagella  (Fig.  2 ID)  and,  rapidly 
multiplying,  undergo  a  crithidial  stage.  As  multiplication  con- 
tinues free-swimming  trypanosome  forms   are   again   produced 


To  cerebrospinal    fluid  cau&in^  sleeping 
dlckness  and  deaih. 


Transmission  by 
bite  of  tsetse  fJLy. 


t 


Trypanosomes 

in      human      blood  causing 
Trypanosome  j^^^r. 

Transmission  by  bfe 
Man, Antelope,  etc.  [  of  tsetse  fly. 


Forms  in  5a[Wary  glands 
ready  for  re.  infection. 
\20"'-50*''  day) 


Tsetse  riy 


Crltbidial  /ortns  in 
salivacy  jglands 
(2.  or  v3  days  later) 


Forms  in  midgut,{V5/ 
offer  infective  meal). 


newly  arrh/ed  form  in 
^afivary  aland. 
(l2*htoJo*;'day6.) 


Fig.  21. 


Lona  slender  forms  In  proventricutas. 
("about  I0*'«tol5**'days) 

Life  History  of  Trypanosoma  gambiense.      X  1500.     (Constructed 
from  figures  by  Miss  Robertson.) 


which  very  closely  resemble  the  parasites  in  vertebrate  blood 
(Fig.  21 E)  and  which  are  now  capable  of  infecting  a  vertebrate 
host.  The  whole  cycle  in  the  fly  usually  occupies  from  20  to  30 
days.     According  to  Kinghorn  and  Yorke  the  time  required  for 


DEVELOPMENT  IN  MAN 


101 


Glossina  morsitans  to  become  infective  varies  from  11  to  25  days, 
but  under  unfavorable  conditions  the  parasites  may  remain  in 
the  fly  in  an  incomplete  stage  of  development  for  at  least  two 
months.  A  temperature  between  75°  F.  and  85°  F.  is  necessary 
for  the  full  development  of  the  parasite  n  the  fly,  ending  in 
invasion  of  the  salivary  glands.  For  two  days  after  the  trypa- 
nosomes  have  been  swallowed  by  the  fly  they  remain  infective  if 
injected  into  a  vertebrate,  but  after  this  time  they  must  pass 
through  the  crithidial  stage  before  they  are  again  infective. 

The  reader  will  note  that 
no  sexual  reproduction, 
such  as  is  so  conspicuous  in 
the  mosquito  cycle  of  the 
malarial  parasites,  has  been 
described  in  this  fly  cycle 
of  the  trypanosome,  though 
the  general  features  of  the 
cycle  are  so  parallel.  It 
can  hardly  be  doubted  that 
sexual  reproduction  of  some 
kind,  or  at  least  something 
which  takes  the  place  of  it, 
does  occur  in  the  tsetse  fly, 
but   it    has '  not   yet   been 

recognized  by  scientific  ob-        Fig.   22.     Method  of  division  in  trypano- 

somes.     A,  elongated  form  ready  for  division; 
B,  form  with  divided  parabasal  body  and  par- 
Life  Cycle  in  Man. — The    tially  split  undulating  membrane;  C,  form  with 
nnrfl^ifp*^        whpn      iniPpfpH    ^""^^^^    parabasal    body,    double    undulating 
parasites,       wnen      mjeciea    membrane,    and    double  nucleus;    D,    almost 
into  man  or  other  SUSCepti-    completely  divided  forms,  adhering  by  poste- 

ble  animals  by  a  tsetse  fly, 

live  and  multiply  in  the  blood,  swimming  free  in  the  serum  with- 
out entering  the  corpuscles  (Fig.  21  A).  They  obtain  nourishment 
by  simply  absorbing  food  material  through  the  delicate  cuticle  which 
covers  them.  The  method  of  division  is  the  usual  protozoan  type  of 
simple  fission.  When  about  to  divide  the  trypanosome  elongates 
(Fig.  22A)  and  the  parabasal  body  at  the  posterior  end  divides 
first  (Fig.  22B).  Then  the  flagellum  and  undulating  membrane 
begin  to  split  from  the  posterior  end  forward,  the  central  nucleus 
divides  (Fig.  22C),  and  the  animal  splits  into  two  parts  which  hang 
together  longest  by  the  ''snouts"  or  posterior  ends  (Fig.  22D). 


102  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

The  fast-multiplying  parasites  do  not  remain  in  the  blood  of 
their  victim  but  penetrate  many  of  the  tissues  and  organs  of 
the  body,  especially  the  liver,  spleen,  lungs  and  lymph  vessels 
and  glands.  The  last  mentioned  are  probably  one  of  the  main 
strongholds  of  the  parasite  in  the  body  and  the  swelling  of 
lymph  glands,  especially  in  the  neck,  has  already  been  men- 
tioned as  one  of  the  characteristic  symptoms  of  sleeping  sickness. 
The  parasites  are  not  present  in  constant  numbers  in  the  blood, 
but  periodically  appear  in  large  numbers  and  then  apparently 
disappear  at  fairly  regular  intervals.  Often  the  trypanosomes 
are  so  few  in  the  blood  that  their  presence  can  be  proved  only  by 
causing  disease  through  the  injection  of  some  of  the  blood  into  a 
susceptible  animal  or  by  causing  the  parasites  to  multiply,  as 

they  will  quite  readily  do,  in  a 
suitable  artificial  culture  me- 
dium. In  Nigeria  the  parasites 
are  hardly  ever  seen  in  the  blood 
of  infected  persons,  but  they  can 
be  found  by  puncturing  a  lymph 
gland.  According  to  recent 
investigations  by  Fantham  the 
trypanosomes,  probably  as  a  re- 
action against  antibodies  which 
tend  to  destroy  them*,  shrink  into 
Fig.  23.    Agglutination  of  trypano-  rounded  sporehke   bodies  with- 

somes,  T.  lewxsi,  in  blood  of  immunized  i  •  i 

rat.     (After  Laveran  and  Mesnil.)  OUt  locomotory  Organs  but  With 

a  protective  shell.  In  this 
condition  they  remain  until  conditions  again  become  favorable 
for  them  when  they  once  more  elongate,  develop  a  flagellum  and 
undulating  membrane,  multiply  and  reappear  in  the  circulating 
blood.  After  several  months  or  years  the  parasites  penetrate 
the  cavity  of  the  brain  and  spinal  cord  and  Hve  in  the  cerebro- 
spinal fluid  which  fills  it;  this  invasion  of  the  central  nervous 
system  is  the  direct  cause  of  the  dread  sleeping  sickness  stage  of 
the  disease. 

While  under  normal  and  favorable  conditions  the  trypanosomes 
merely  live  and  multiply  in  the  way  described  above,  they  are 
capable  of  reacting  in  a  very  peculiar  manner  when  exposed  to 
unfavorable  conditions,  such  as  the  presence  of  drugs,  low  tem- 
perature or  administration  of  serum  from  an  immune  animal. 


COURSE  OF  SLEEPING  SICKNESS  103 

Under  such  circumstances  they  have  a  tendency  to  mass  together 
in  large  numbers,  up  to  a  hundred  or  more,  hke  sheep  in  a  storm, 
all  with  their  flagellated  ends  projecting  from  a  common  center 
(Fig.  23).  Such  '^  primary  agglomerations  "  may  adhere  to  form 
''  secondary  agglomerations  "  comprising  altogether  many  hun- 
dreds of  parasites.  When  the  unfavorable  conditions  disappear, 
the  trypanosomes  disentangle  themselves  without  any  apparent 
ill  effects,  although  a  few  of  them  remaining  agglutinated  may 
die  and  disintegrate.  Another  peculiar  habit  described  by  some 
investigators  is  the  extrusion  from  their  bodies  of  very  minute 
granules,  really  tiny  buds  from  the  nucleus,  which  ultimately 
develop  into  new  trypanosomes.  This  is  said  to  occur  just  be- 
fore the  temporary  disappearance  of  the  trypanosomes  from  the 
blood. 

The  Disease.  —  The  course  of  the  disease  caused  by  trypano- 
some  infection  is  insidious  and  irregular  in  the  extreme.  The 
Gambian  and  Rhodesian  diseases  are  essentially  alike  in  their 
symptoms  and  in  the  course  they  run,  except  that  the  latter  is 
usually  more  rapid  in  development  and  more  virulent  in  effect, 
as  a  rule  causing  death  within  three  or  four  months  after  in- 
fection. The  variety  of  the 
Gambian  disease  found  in 
Nigeria  is  comparatively  mild 
and  of  long  duration. 

The  bite  of  an  infected  tsetse 
fly  is  usually  followed  by  itching 
and  irritation  near  the  wound. 
After  a  few  days  fever  is  felt 
and  a  peculiar  tenderness  of  the 
muscles  develops,  so  that  strik- 
ing against  an  object  causes 
undue  pain.  Usually  the  fever 
comes  and  goes  at  irregular  in- 
tervals of  days  or  weeks  or  even  Fig.  24.  Negro  infected  with  trypano- 
months,  an  infected  person  f^es,  showing  enlarged  cervical  glands. 
.  .  ^  (After  KoUe  and  A\  assemiann.) 

sometimes   carrymg  the  para- 
sites in  his  blood,  as  shown  by  its  infectivity  when  injected  into 
susceptible  animals,  for  months  at  a  time  without  any  appreciable 
fever,  and  in  insufficient  numbers  to  be  seen  readily  by  microscopic 
examination.     When  the  attacks  of  typical  trypanosome  fever  do 


104  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

come  they  generally  are  worse  in  the  evening,  unlike  malarial  fevers. 
After  a  variable  time  the  victim  becomes  weak  and  anemic,  probably 
due  to  toxins  secreted  by  the  parasites,  his  pulse  becomes  rapid, 
and  various  lymph  glands,  especially  those  of  the  neck,  tend  to 
swell  up  and  become  tender.  Often  an  irritating  rash  breaks  out 
on  the  skin  during  the  early  stages  of  the  disease.  Loss  of  am- 
bition and  vitahty  usually  figure  prominently,  and  childbirth 
is  seriously  interfered  with.  It  is  possible  that  after  weeks  or 
months  or  years  of  irregular  fever  and  debihty  the  disease  may 
spontaneously  disappear,  and  never  become  more  than  trypano- 
some  fever.  Usually,  however,  the  parasites  ultimately  succeed  in 
penetrating  to  the  cerebrospinal  fluid  in  the  cavity  of  the  brain 
and  spinal  cord,  and  "  sleeping  sickness  "  results.  In  some  cases 
the  onset  of  this  horrible  disease  has  been  known  to  be  delayed 
for  seven  years  after  the  beginning  of  the  disease,  but  usually  it 
comes  in  the  course  of  a  few  months. 

Sleeping  sickness  is  ushered  in  by  an  increase  in  the  general 
physical  and  mental  depression,  the  symptoms  being  not  unhke 
those  of  hookworm  disease  but  more  pronounced.  The  victim 
wants  to  sleep  constantly  and  lies  in  a  stupor;  his  mind  works 
very  slowly,  and  even  the  slightest  physical  .exertion  is  obnoxious. 
Eventually  the  sleepiness  gets  such  a  hold  on  him  that  he  is 
likely  to  lose  consciousness  at  any  time  and  even  neglects  to  swal- 
low his  food.  After  weeks  of  this  increasing  drowsiness,  his 
body  becomes  emaciated,  a  trembling  of  the  hands  and  other 
parts  of  the  body  develops,  with  occasional  muscular  convulsions 
and  sometimes  maniacal  attacks.  He  finally  passes  into  a  state 
of  total  loss  of  consciousness  ending  in  death,  or  death  may  end 
the  unhappy  condition  earlier  during  an  unusually  intense  con- 
vulsion or  fever,  or  through  the  agency  of  some  complicating 
disease.  If  untreated,  death  is  the  inevitable  outcome.  A 
large  per  cent  of  infections  occur  among  people  of  middle  age. 
Old  people  are  significantly  few  in  number  in  sleeping  sickness 
districts.  The  presence  of  these  few  may  be  due  to  a  natural 
or  acquired  immunity.  In  Nigeria  the  disease  predominates  in 
young  people,  possibly  because  they  are  water-carriers  and  are 
therefore  more  exposed  to  the  bites  of  tsetse  flies. 

Treatment.  —  Various  drugs  have  been  tried  in  the  treatment 
of  trypanosomiasis,  especially  arsenic  and  antimony  compounds. 
Until  recently  the  most  effective  drugs  in  use  have  been  arsenic 


TREATMENT  OF  SLEEPING  SICKNESS  105 

in  the  form  of  atoxyl  or  salvarsan,  injected  intramuscularly,  or 
antimony  in  the  form  of  tartar  emetic,  injected  intravenously. 
Atoxyl  is  injected  in  weak  solution,  the  doses  being  repeated 
every  few  days  for  a  period  of  many  months,  even  long  after  the 
symptoms  of  the  disease  have  disappeared.  A  serious  objection 
to  atoxyl  is  the  slight  tolerance  which  many  people  have  for  it, 
and  its  serious  effects  on  the  optic  nerve  and  digestive  apparatus. 
Tartar  emetic  is  also  injected  in  weak  solutions,  care  being  taken 
not  to  allow  it  to  escape  into  the  muscles  or  connective  tissues, 
to  which  it  is  very  irritating.  Usually  a  high  fever  follows  the 
administration  of  either  drug,  probably  due  to  toxic  substances 
liberated  from  dead  trypanosomes.  Recently  the  Rockefeller 
Institute  has  produced  a  new  arsenic  compound,  tryparsamide, 
which  promises  to  be  more  valuable  than  any  other  drug  yet  tried. 
It  is  very  soluble  in  water,  can  be  given  either  intramuscularly 
or  intravenously,  produces  practically  no  untoward  effects,  ef- 
fects very  rapid  destruction  of  the  parasites  in  the  blood,  brings 
about  very  marked  improvement  in  the  condition  of  the  spinal 
fluid  in  advanced  cases,  and  results  in  remarkable  general  ben- 
eficial effects. 

The  chief  difficulty  in  the  use  of  any  of  these  drugs  is  that  the 
trypanosomes  tend  to  build  up  a  tolerance  for  them,  in  much 
the  same  way  that  a  man  may  build  up  a  tolerance  for  opium 
or  other  drugs.  This  tolerance  is  hereditary  and]  gives  rise  to 
"  arsenic-fast  "  or  "  antimony-fast  "  strains  of  trypanosomes. 
In  such  cases  the  parasites  cannot  be  destroyed.  It  is  an  inter- 
esting fact  that  in  at  least  one  species  of  trypanosome,  T.  lewisi 
of  rats  and  mice,  and  probably  others  as  well,  when  strains  im- 
mune to  atoxyl  are  passed  through  their  intermediate  host,  a 
louse,  where  they  presumably  undergo  sexual  reproduction  or 
some  process  which  takes  its  place,  the  tolerance  is  entirely  lost. 
Thus  the  sexual  process  at  a  stroke  ehminates  acquired  charac- 
ters which  have  been  maintained  through  thousands  of  asexual 
generations  in  passages  from  mouse  to  mouse  or  from  rat  to  rat. 
This  fact,  if  invariably  true,  is  of  considerable  importance  in 
the  outlook  for  the  treatment  of  sleeping  sickness,  since  it  would 
prevent  what  would  otherwise  inevitably  happen,  the  evolution 
of  a  permanent  strain  of  trypanosomes  immune  to  both  arsenic 
and  antimony.  The  fact  that  parasites  resistant  to  arsenic  may 
not  be  resistant  to  antimony,  and  vice  versa,  makes  it  advisable 


106  TRYPANOSOMES  AND   SLEEPING  SICKNESS 

in  treating  trypanosome  fever  to  give  both  drugs  either  to- 
gether or  alternately. 

When  the  disease  has  reached  the  sleeping  sickness  stage 
and  the  parasites  have  penetrated  the  cerebrospinal  fluid,  a 
cure  has  so  far  never  been  accomplished.  The  arsenic  and  anti- 
mony compounds  which  are  so  destructive  to  trypanosomes 
will  not  permeate  the  nervous  tissue  and  diffuse  into  the  cerebro- 
spinal fluid,  and  they  are  too  poisonous  to  be  injected  into  the 
spinal  canal.  The  success  that  has  been  attained  in  the  use  of 
salvarsanized  serum  (see  p.  57)  against  spirochsetes  in  the  cere- 
brospinal canal  gives  hope  that  a  similar  mode  of  treatment  may 
be  used  in  the  case  of  sleeping  sickness.  All  that  can  be  done 
for  sleeping  sickness  now  is  to  alleviate  the  suffering  and  postpone 
the  inevitable  end. 

Although  the  use  of  immune  serum  from  animals  which  have 
recovered  has  been  very  successful  in  curing  and  immunizing 
various  lower  animals  against  certain  trypanosome  diseases,  this 
has  not  yet  been  accomplished  for  man. 

The  Rhodesian  trypanosome  consistently  resists  both  arsenic 
and  antimony  treatment,  and  no  successful  drug  has  been  found 
for  combating  this  parasite. 

Prevention.  —  Since  the  tsetse  flies,  Glossina  palpalis  and  G. 
morsitans,  are  by  all  odds  the  most  important  means  of  trans- 
mitting the  Gambian  and  Rhodesian  trypanosomes  respec- 
tively, the  prevention  of  the  diseases  resolves  itself  into  the  prob- 
lem of  avoiding  or  exterminating  these  insects.  Methods  for 
controlhng  and  destroying  tsetse  flies  are  discussed  in  the  chap- 
ter on  Biting  Flies,  p.  501. 

In  places  where  tsetse  fly  extermination  has  not  or  cannot  be 
accomplished  the  best  safeguard  is  the  avoidance  of  the  ''  fly- 
belts."  In  the  case  of  G.  palpalis  these  belts  consist  of  narrow 
strips  along  the  brushy  edges  of  water,  but  with  G.  morsitans 
they  are  not  so  closely  limited,  the  flies  being  sometimes  found 
at  considerable  distances  from  water.  Villages  or  camps  should 
always  be  removed  from  fly-belts,  and  travel  through  the  belts, 
when  absolutely  necessary,  should  be  done  on  dark  nights  when 
the  flies  seldom  bite.  Occupations  carried  on  in  fly-infested 
areas  should  be  discouraged  or  prohibited.  In  Uganda  fishing 
along  the  fly-infested  streams  and  lake  shores  is  one  of  the  chief 
occupations  indulged  in  by  the  natives,  who  go  naked  and  are 


PREVENTION  OF  SLEEPING  SICKNESS  107 

constantly  bitten.  The  deadly  epidemic  of  sleeping  sickness  in 
Uganda  was  fostered  by  the  fishing  industry.  It  has  been  sug- 
gested that  by  importing  dried  sea  fish  to  trade  for  agricultural 
products  the  natives  might  be  induced  to  change  their  occu- 
pation. In  Congo  the  rubber  industry  is  the  one  which  is  the 
most  deprecated.  Personal  protection  against  tsetse  flies  is  dis- 
cussed on  page  501. 

Another  method  of  protection  is  suggested  by  the  researches 
of  Van  den  Branden  who  has  found  that  a  single  injection  into 
the  veins  of  salvarsan  or  neosalvarsan  or  some  of  their  compounds 
will  sterilize  the  blood  against  trypanosomes  for  a  period  of  several 
months  —  in  the  case  of  salvarsan  copper  for  19  to  24  months. 

Infected  individuals  should  not  only  be  kept  away  scrupulously 
from  places  where  flies  can  possibly  get  access  to  them,  but  should 
also  be  prevented  from  traveling  to  new  places.  Some  strains 
of  trypanosomes  seem  to  be  much  more  virulent  than  others, 
and  the  introduction  of  a  virulent  strain  to  a  region  where  a 
mild  strain  previously  existed  has  occasionally  caused  a  con- 
siderable increase  in  the  disease.  The  strict  quarantine  of  in- 
fected persons,  while  unquestionably  worth  while,  is  not  a  meas- 
ure sufficient  to  stamp  out  the  disease,  since  many  of  the  wild 
animals  of  Africa  serve  as  reservoirs  for  the  disease,  harboring 
the  parasites  in  their  blood  but  not  succumbing  to  them.  Tsetse 
flies  on  the  shores  and  islands  of  Lake  Victoria,  after  the  entire 
population  had  been  stringently  kept  away  for  three  years  so 
that  the  flies  could  not  have  fed  on  human  blood  during  this  time, 
were  found  to  be  still  infective.  The  situtunga  antelope  and 
other  wild  game  undoubtedly  served  as  a  reservoir.  It  has  been 
suggested  that  a  war  of  extermination  be  made  on  the  rich  and 
interesting  wild  game  of  the  countries  infected  with  the  Rho- 
desian  trypanosome  in  the  hope  of  checking  the  rapid  spread  of 
the  disease  (see  p.  503).  It  has  recently  been  shown  by  Taute, 
however,  that  a  large  proportion  of  the  wild  game  of  Nyasa- 
land  is  infected  with  a  trypanosome  indistinguishable  from 
Trypanosoma  rhodesiense  in  all  its  general  characters  but  non- 
pathogenic to  man.  Taute  evidently  had  the  courage  of  his 
convictions  since  he  tried  several  times  to  infect  himself  with 
this  trypanosome  without  success.  It  is  possible,  however,  that 
a  high  natural  immunity  to  the  parasite  may  exist  in  many  people, 
and  thus  explain  Tautens  negative  results. 


108  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

Probably  the  deadly  Trypanosoma  rhodesiense  is  merely  a  strain 
of  this  wild  game  trypanosome  which  has  undergone  some 
physiologic  change  or  mutation,  making  it  possible  for  it  to  live 
in  the  human  body.  Bruce  and  some  others  consider  it  identical, 
in  every  respect  except  its  ability  to  live  in  human  bodies,  with 
the  well-known  and  widespread  T.  brucei  which  causes  nagana  in 
wild  and  domesticated  animals. 

A  concrete  example  of  sleeping  sickness  extermination  is  to  be 
found  in  the  fight  against  it  on  the  Island  of  Principe  by  the 
Portuguese  Sleeping  Sickness  Commission.  Sleeping  sickness 
had  been  a  scourge  on  the  island  for  years  when  the  Commission 
began  its  work  in  1911.  Its  efforts  were  directed  against  the 
tsetse  fly,  but  this  was  accompanied  by  an  active  campaign 
against  pigs,  dogs  and  other  trypanosome  carriers,  and  the 
thorough  care  and  treatment  of  human  victims.  The  methods 
used  are  discussed  in  Chapter  XXVI.  The  Commission  cleared  the 
island  of  sleeping  sickness  in  a  four  years'  campaign,  but  the  tsetse 
flies  are  not  yet  totally  exterminated,  and  the  present  condition 
on  the  island  can  only  be  maintained  by  constant  work  in  the 
future,  though  at  comparatively  slight  cost. 


Chagas*  Disease 

A  very  different  but  hardly  less  destructive  disease  is  caused 
by  a  trypanosome,   Trypanosoma  (or  Schizotrypanum)  cruzi,  in 

certain  parts  of  South  America. 
Chagas,  of  the  Oswaldo  Cruz 
Institute,  first  investigated  the 
disease  in  the  state  of  Minas 
Geraes  in  Brazil.  He  found  that 
nearly  all  children  in  the  endemic 
regions  were  stricken  with  the 
disease,  usually  before  they  were 

Fig.  25.    Trypanosoma  cruzi  in  blood  i  ^        rr^i  i    ^•l 

of    experimentally    infected    monkey.    O^e  year  old.      The  mortality  WaS 

A,  so-called  male  form;  B,  so-called  found  to  be  very  high,  and  those 

female  form.     (After  Chagas.)  ,  -1^1         •    • .  •    i 

who  survived  the  initial  acute 
attack  usually  passed  over  into  a  chronic  diseased  condition,  very 
often  being  left  to  live  a  worse  than  useless  life  as  paralytics, 
idiots  or  imbeciles.  The  disease  has  since  been  found  in  other 
parts  of  Brazil  and  in  neighboring  countries.     Large  bloodthirsty 


CHAGAS'   DISEASE  —  PARASITE  IN   MAN 


109 


bugs  of  the  genus  Triatoma  serve  as  intermediate  hosts;  bugs  of 
a  number  of  species  infected  with  trypanosomes  morphologically 
indistinguishable  from-T.  cruzi  have  been  found  all  the  way  from 
Central  America  to  Argentina,  but  the  disease  in  man  has  been 
recognized  only  in 
a  small  part  of 
this  extensive  area, 
though  it  is  sus- 
pected of  existing 
in  northern  Argen- 
tina and  may  oc- 
cur in  many  more 
places  than  is  now 
known. 

Human  Cycle. — 
The  trypanosome 
causing  this  disease 
very  closely  resem- 
bles the  sleeping 
sickness  trypano- 
somes in  form  but 
it  is  quite  different 
in  its  life  history. 
In  the  human  body, 
Chagas  recognized 
two  distinct  types 
which  he  believed 
to  be  male  and  fe- 
male forms,  but 
subsequent  work 
indicates  that  these  n 
two 

merely    young    and    capillary;  unpar.  c,  unparasitized  cells.     X  1000.    (After 

adult  forms  of  the 
parasite.  Unlike  other  trypanosomes  this  species  as  found  in 
the  blood  never  exhibits  stages  in  division,  and  this  fact  led 
Chagas  to  search  for  some  other  form  of  multiplication.  He 
found  in  the  lungs  of  infected  animals  what  he  thought  to  be 
a  process  of  division  of  the  trypanosomes  into  eight  parts,  but 
this  later  was  found  to  be  a  stage  in  the  life  history  of  an  entirely 


Fig.  26.    Trypanosoma  cruzi.    A,  cyst  containing  Leish- 
mania  forms  in  muscle  fiber  of  guinea-pig,  cross  section; 
nucleus  of  muscle  fiber.     B,  older  cyst,   containing 
.  trypanosome  forms,  in  neuroglia  cell  in  gray  matter  of 

types     are    cerebrum;    n.,  nucleus  of  parasitized  cell;    bl.  cap.,  blood 
capillary : 
Vianna.) 


no  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

different  parasite.  The  real  method  of  multipHcation  was  first 
discovered  by  Vianna  in  the  bodies  of  man  and  animals  who  had 
died  of  the  disease.  Vianna  found  in  various  tissues,  especially  in 
the  walls  of  the  heart,  the  striped  muscles,  the  central  nervous 
system  and  various  glands,  greatly  swollen  cells  which  served  as 
cysts,  enclosing  a  mass  of  rapidly  dividing  trypanosomes,  varying 
in  number  from  just  a  few  to  many  hundreds.  In  younger  cysts 
the  parasites  are  round  in  form  and  exactly  resemble  Leishman 
bodies  (Fig.  26 A),  while  in  older  cysts  the  flagellum  can  be  seen 
on  many  individuals  and  the  trypanosome  form  becomes  evident 
(Fig.  26B).  When  the  enclosing  cell  has  swollen  to  the  bursting 
point,  the  swarming  mass  of  trypanosomes  is  liberated.  Each 
parasite,  unless  destroyed,  then  penetrates  a  new  cell  somewhere 
in  the  body,  usually  near  where  it  originated,  and  begins  the 
process  of  reproduction  again.  Only  in  the  early  acute  stage  of 
the  disease  can  the  parasites  live  in  the  blood,  since  the  blood 
serum  rapidly  reacts  by  the  formation  of  antibodies,  and  be- 
comes deadly  to  trypanosomes.  Chagas  believed  that  the  para- 
sites could  hve  within  the  corpuscles  as  well  as  in  the  serum,  but 

later  work  does  not  confirm  this. 
On  account  of  the  development  of 
antibodies  in  the  blood  serum,  the 
parasites  are  very  seldom  found  in 
the  blood  of  chronic  cases  of  the 
disease,  though  their  cysts  may  be 
abundant  in  various  tissues  and 
glands  in  the  body. 

Fig.    27.        Trypanosoma    cruzi    in         Life   Cycle  in  BugS,  and  TronS- 

biood  of  ape  said  to  be  inside  cor-  mission.  —  The  intermediate  host 

puscles.     (After  Chagas.) 

of  Trypanosoma  cruzi  is  a  large 
black  and  red  bug,  Triatoma  megista,  known  to  the  natives  as 
*'barbeiro."  It  is  related  to  the  cone-nose,  Triatoma  sanguisuga, 
of  our  southern  states.  The  barbeiro  is  a  fierce  blood-sucking 
insect  which  infests  the  dirty  thatched  or  mud  houses  of  the 
natives,  coming  out  at  night  and  skillfully  secreting  itself  in  the 
daytime  (see  p.  379,  and  Fig.  168). 

It  was  found  that  the  bugs  in  the  houses  where  Chagas'  disease 
had  been  observed  were  invariably  infected  with  trypanosomes 
in  their  gut,  and  from  this  fact  and  from  the  habits  of  the  bug 
Chagas  rightly  deduced  and  later  proved  that  the  bug  was  the 


CHAGAS'   DISEASE  —  PARASITE  IN  BUG 


111 


transmitting  agent  of  the  trypanosome.  A  few  hours  after  a 
bug  has  fed  on  infected  blood  the  trypanosomes  begin  to  change 
form  in  the  midgut,  becoming  round  and  Leishmania-like  in  form, 
losing  the  flagellum  and  undulating  membrane  (Fig.  28A,  B  and 
C.)  Then  comes  a  period  of  very  rapid  increase  in  number,  the 
parasites  gradually  pushing  backward  toward  the  hindgut  by 
sheer  multiplication.  After  about  two  days  Crithidia  forms 
begin  to  develop  and  become  numerous  in  the  hindgut,  being 


Fig.  28.  Development  of  Trypanosoma  cruzi  in  digestive  tract  of  bug  (Tria- 
toma  megista).  A,  freshly  ingested  form;  B,  rounding  up  and  loss  of  flagellum,  6 
to  10  hrs.  after  ingestion;  C,  Leishmania-\\^e  form  in  midgut,  10  to  20  hrs.  after 
ingestion;  D,  redevelopment  of  flagellum  and  undulating  membrane,  21  hrs.  after 
ingestion;  E  and  F,  crithidial  forms  in  hindgut,  25  hrs.  after  ingestion;  G,  trypa- 
nosome form  from  salivary  gland.  8  days  or  more  after  ingestion.    (After  Chagas.) 


voided  with  the  excrement  from  time- to  time  (Fig.  28D,  E  and  F). 
It  has  been  suggested  that  these  crithidial  forms  do  not  play  any 
part  in  the  transmission  of  the  disease  to  man  but  that  they  rep- 
resent a  return  to  a  primitive  condition  suited  to  existence  in  the 
bugs,  and  that  they  may  be  transmitted  from  bug  to  bug  in  this 
form,  since  the  bugs  are  known  to  prey  to  some  extent  upon  each 
other  and  a^so  upon  their  excrement.  Torres,  however,  considers 
transmission  of  the  flagellates  from  bug  to  bug  as  very  doubtful. 
Chagas  believes  that  there  is  a  second  cycle  of  development  in 


112  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

the  bugs  which  he  interprets  as  sexual  reproduction.  After  about 
ten  days  there  occasionally  occurs  in  the  midgut  of  the  bugs 
round  organisms  with  thick  capsules,  and  in  a  few  cases  Chagas 
has  observed,  after  about  six  days,  what  seemed  to  be  a  division 
of  this  body  into  eight  individuals  each  presumably  giving  rise 
to  a  trypanosome  of  a  new  generation.  Whether  or  not  the 
infective  trypanosomes  arise  in  this  way  they  appear  in  the  mid- 
gut from  the  eighth  day  onward.  The  occurrence  of  the  infective 
parasite  in  the  salivary  glands  (Fig.  28G)  is  very  irregular.  The 
fact  that  parasites  have  occasionally  been  found  in  the  body 
cavity  of  bugs  suggests  that  the  trypanosomes  may  make  their 
way  through  it  to  reach  the  salivary  glands.  As  already  re- 
marked the  trypanosomes  in  the  bugs  have  never  been  found 
infective  before  the  eighth  day,  but  once  the  infective  forms  have 
developed  they  persist  in  the  bugs  for  over  a  year. 

The  barbeiro  is  not  the  only  insect  capable  of  acting  as  an 
intermediate  host  for  Trypanosoma  cruzi.  Several  other  South 
and  Central  American  species  of  Triatoma  have  been  found  to 
be  naturally  infected  with  this  trypanosome  or  with  one  mor- 
phologically indistinguishable  from  it,  and  experimentally  the 
trypanosomes  develop  in  the  cosmopolitan  species,  T.  ruhro- 
fasdata  and  other  cone-noses  and  in  bedbugs.  Nor  is  man  the 
only  vertebrate  host.  Experimentally  apes,  dogs  and  guinea- 
pigs  are  subject  to  infection,  and  in  nature  the  common  Bra- 
zilian armadillo,  Dasypus  novemcindus,  and  various  rodents  have 
been  found  infected,  their  infection  undoubtedly  being  carried 
by  the  common  bug,  Triatoma  geniculata,  which  infests  their 
burrows.  The  fact  that  infected  bugs  occur  in  some  places 
where  Chagas'  disease  is  not  known  to  occur  suggests  that,  as  is 
the  case  with  Trypanosoma  rhodesiense  and  the  trypanosomes 
undistinguishable  from  it  except  by  their  harmlessness  to  man, 
not  all  strains  of  the  parasite  cause  human  disease.  It  is  inter- 
esting to  note  that  a  very  similar  trypanosome  has  recently  been 
discovered  by  Kofoid  and  McCulloch  in  Triatoma  protracta  of 
southwestern  United  States.  This  bug  is  common  in  nests  of 
wood-rats  and  frequently  attacks  man  also.  This  discovery 
suggests  one  of  two  things:  either  the  trypanosome  described 
as  T.  triatomce,  and  which  is  admitted  by  the  discoverers  to  differ 
from  T.  cruzi  only  in  sUght  characteristics  of  questionable  im- 
portance, is  really  identical  with  or  a  mere  variety  of  T.  cruzi, 


COURSE  OF  CHAGAS'   DISEASE  113 

or  else  others  of  the  trypanosomes  observed  in  species  of  Triatoma 
from  Argentina  to  Central  America  may  not  be  identical  with 
the  trypanosome  which  is  the  cause  of  Chagas'  disease. 

The  Disease.  —  In  endemic  regions  Chagas'  disease  is  so 
prevalent  that  children  are  usually  attacked  within  a  few  months 
after  birth,  and  at  this  tender  age  are  often  unable  to  withstand 
its  effects.  If  death  does  not  result  the  disease  passes  over  into 
one  or  other  of  its  various  chronic  forms.  As  a  result  it  is  very 
rare  to  find  acute  cases  in  anyone  but  young  children  or  new 
arrivals.  The  latter,  however,  usually  come  from  other  infected 
regions  and  show  marks  of  the  chronic  disease,  and  so  are  not 
susceptible  to  a  new  acute  infection. 

The  acute  infection  is  marked  by  a  constant  high  fever,  lasting 
from  ten  to  thirty  days,  often  without  remission,  and  by  a  charac- 
teristic swollen  face,  noticeable  from  a  considerable  distance. 
The  skin  has  a  pecuUar  feeling  of  ''  crepitation  "  due  to  the 
mucous  infiltration  of  the  tissue  under  the  skin.  The  lymph 
glands  especially  in  the  neck  and  arm  pits  swell  up,  the  liver  and 
spleen  become  enlarged,  and  the  thyroid  gland  becomes  swollen 
as  in  goitre.  In  fact,  most  of  the  symptoms  are  connected  with 
interference  with  the  thyroid  gland  which,  while  becoming 
massive  in  size,  becomes  reduced  in  function,  thereby  causing  a 
number  of  nervous  and  constitutional  symptoms.  This  inter- 
ference is  due,  apparently,  not  so  much  to  invasion  by  the  para- 
sites as  to  a  specific  effect  of  the  toxins  produced  by  them  and 
carried  by  the  blood.  These  are  the  constant  features  of  the 
disease;  the  other  symptoms  vary  according  to  the  localization 
of  the  parasites.  Frequently  they  multiply  in  the  heart  muscles, 
and  the  functions  of  the  heart  may  be  seriously  interfered  with. 
Very  often,  and  with  the  most  dire  results,  the  parasites  invade 
the  brain  and  spinal  cord.  When  this  happens  the  mortality  is 
high,  and  it  is  only  a  pity  that  it  is  not  higher,  since  it  would 
be  better  if  death  always  eliminated  these  unfortunate  trypano- 
some victims  who  are  spared  only  for  an  unproductive,  piteously 
mutilated  life,  doomed  to  grow  up  with  the  intellect  of  an  infant, 
or  as  paralytics,  idiots  or  imbeciles. 

The  chronic  forms  of  the  disease  follow  the  acute  form  by  the 
development  of  a  substance  in  the  blood  which  is  deadly  to  the 
trypanosomes,  so  that  the  latter  are  restricted  to  the  protecting 
tissue  cells  in  which  they  multiply.     The  commonest  chronic 


114  TRYPANOSOMES  AND  SLEEPING  SICKNESS 

form  is  that  in  which  the  predominating  symptoms  result  from 
an  enlarged  but  insufficient  thyroid  gland — goitre,  cretinism,  con- 
vulsions, swollen  skin  and  various  functional  disturbances,  includ- 
ing imperfect  heart  and  intellectual  defects.  Another  chronic  form 
is  that  in  which  the  heart  is  especially  affected.  The  fact  that 
the  parasites  have  a  special  predilection  for  the  heart  muscles 
makes  this  form  of  the  disease  very  common.  The  results  of  locali- 
zation of  the  parasites  in  the  nervous  system  have  already  been 
mentioned.  The  intensity  of  the  motor  disturbances,  varying 
from  paralysis  or  spasmodic  convulsions  of  a  single  muscle  to 
complete  paralysis  or  convulsions  of  the  whole  body,  has  no  rela- 
tion to  the  degree  of  intellectual  affection,  which  may  vary  from 
a  simple  cretinoid  condition  to  complete  idiocy  or  infantilism. 

It  is  doubtful  whether  the  disease  is  ever  recovered  from  entirely 
if  left  to  run  its  course.  Sometimes  the  symptoms  become 
gradually  less  intense,  in  other  cases  they  become  worse  and  new 
ones  develop,  or  recurrences  of  acute  symptoms  may  develop, 
due  either  to  reinfection  or  to  a  loss  of  the  trypanocidal  power  of 
the  blood. 

Treatment  and  Prevention.  —  The  treatment  of  Chagas'  dis- 
sease  is  still  in  the  experimental  stage  but  there  is  some  evidence 
that  tartar  emetic  may  prove  to  be  of  great  value  in  deaUng  with 
it,  at  least  in  early  stages.  In  fact  it  was  the  success  obtained  by 
Vianna  in  combating  the  disease  with  tartar  emetic  that  first 
suggested  to  him  its  use  against  Leishmanian  diseases. 

Prevention  of  the  disease  consists  largely  in  avoiding  and  ex- 
terminating the  barbeiros.  It  is  practically  impossible  to  keep 
the  bugs  out  of  mud  or  thatched  houses.  For  this  reason  the  re- 
building of  houses  with  other  material  is  being  urged  everywhere 
in  Brazil  and  with  good  results.  The  town  of  Bello  Herizonte, 
for  example,  which  was  formerly  termed  "  a  nest  of  cretins  "  is 
now  nearly  free  from  Chagas'  disease,  due  to  the  remodeling  of 
the  houses.  People  traveling  through  infected  districts  can 
readily  protect  themselves  by  sleeping  under  mosquito  nets  and 
by  avoiding  the  native  houses.  There  is  said  to  be  no  danger 
of  being  bitten  by  the  bugs  in  daytime  or  in  the  presence  of  arti- 
ficial light,  since  they  come  forth  only  in  the  dark. 

The  extermination  in  the  vicinity  of  villages  of  armadillos  and  of 
the  various  rodents  which  harbor  the  trypanosomes  would  be  a 
valuable  aid  in  the  reduction  of  the  disease. 


CHAPTER  VII 
INTESTINAL    FLAGELLATES    AND   CILIATES 

The  human  intestine  furnishes  a  habitat  for  a  considerable 
number  of  animals  belonging  to  all  four  classes  of  Protozoa, 
though  it  is  not  so  subject  to  such  infections  as  are  the  digestive 
tracts  of  many  lower  animals,  especially  the  ruminants.  By 
far  the  most  important  intestinal  protozoan  of  man  is  an  ameba, 
Endamoeba  histolytica,  discussed  in  connection  with  other  para- 
sitic amebse  in  a  subsequent  chapter.  Probably  next  to  the 
amebse  from  a  pathogenic  point  of  view  should  stand  the  ciliate, 
Balantidium  coli,  which  is,  however,  not  common  in  most  parts 
of  the  world.  The  various  flagellates  of  the  intestine,  from  the 
simple  bi-flagellate  forms,  such  as  Bodo,  Cercomonas  and  Emhado- 
monas,  some  of  which  are  probably  only  accidentally  parasitic,  to 
the  highly  organized  multi-flagellate  forms,  such  as  Trichomonas 
and  Giardia,  which  are  very  common  human  parasites,  differ 
greatly  as  regards  their  pathogenic  importance,  and  opinions 
do  not  agree  concerning  the  importance  of  particular  ones. 

General  Characteristics  of  Intestinal  Protozoa.  —  In  some 
respects  nearly  all  the  Protozoa  which  make  their  home  in  the 
digestive  tracts  of  animals  resemble  one  another.  Nearly  all  of 
them  secrete  for  themselves  resistant  transparent  cysts  which 
protect  them  from  drying  up  or  from  the  presence  of  an  unfa- 
vorable medium.  In  the  encysted  state  intestinal  protozoans  are 
able  to  exist  under  the  unfavorable  conditions  found  outside  the 
body  of  the  host,  and  are  capable  of  remaining  in  this  state  in  a 
sort  of  torpid  condition  for  long  periods  of  time  until  they  gain 
access  to  a  new  host.  The  cysts  of  intestinal  protozoans  are 
analogous  to  the  resistant  eggs  of  intestinal  worms,  and  like 
worm  eggs  their  presence  in  the  faeces  of  infected  persons  serves  as 
a  convenient  means  of  diagnosis.  The  unencysted  protozoans 
which  may  be  carried  out  of  the  intestine  die  quickly  and 
probably  could  not  produce  a  new  infection  even  if  swaUowed 
immediately,  since  in  some  species  at  least  they  are  unable  to 

115 


116  INTESTINAL  FLAGELLATES  AND   CILIATES 

withstand  the  action  of  the  acid  juices  of  the  stomach.  None  of 
tlie  human  intestinal  Protozoa  require  a  second  host  to  transmit 
them  as  do  the  blood-dwelhng  parasites.  While  outside  the 
body  they  remain  dormant  in  their  cysts  for  weeks  or  months 
until  they  can  gain  access  to  a  host  again  through  food  or  water. 
There  is  still  much  doubt  as  to  the  extent  to  which  intestinal 
protozoans  are  confined  to  particular  hosts.  Some  workers 
believe  that  each  animal  has  its  own  species  peculiar  to  it,  and 
that  these  species  are  not  capable  of  infecting  different  hosts. 
Evidence  is  accumulating,  however,  to  show  that  in  some  cases 
at  least  this  is  not  so,  and  that  many  intestinal  protozoans  of 
man  are  able  to  live  in  such  animals  as  rats,  mice  and  hogs. 
Most  intestinal  protozoans  are  of  very  wide  geographic  distri- 
bution, their  abundance  in  any  given  place  being  largely  deter- 
mined by  the  warmth  of  the  climate  and  the  sanitary,  or  rather 
unsanitary,  conditions. 

As  remarked  before  there  has  been  much  discussion  concerning 
the  effect  produced  by  various  species  of  flagellates  in  the  in- 
testine. Naturally  these  parasites  are  seldom  discovered  except 
when  there  is  some  intestinal  ailment,  since  in  normal  health 
faeces  are  seldom  submitted  for  examination.  Where  routine 
examinations  have  been  made  regardless  of  physical  condition, 
it  has  been  found  that  a  large  per  cent  of  people  in  unsanitary 
places  are  infected.  Stiles,  in  a  town  in  one  of  our  southern 
states,  found  that  from  50  to  100  per  cent  of  the  children  were 
infected,  and  it  would  probably  be  easily  within  the  bounds  of 
truth  to  say  that  75  per  cent  of  all  people  in  warm  countries  liv- 
ing in  places  where  unsanitary  conditions  prevail  are  subject 
to  infection  with  one  or  several  species  of  intestinal  Protozoa. 
As  Stiles  has  pointed  out,  such  infection  usually  means  that  the 
infected  person  has  swallowed  human  excrement,  since  it  would  be 
impossible  for  any  natural  agency  to  separate  the  microscopic 
protozoan  cysts  from  the  faeces  in  which  they  are  found.  This 
fact,  impressed  upon  the  mothers  of  infected  children,  especially 
when  accompanied  by  the  remark  that  one  could  not  tell  whether 
the  infection  had  come  from  the  excrement  of  a  white  or  a  negro, 
was  found  by  Stiles  to  be  one  of  the  most  powerful  means  of 
improving  sanitary  conditions  in  the  South. 

Facts  which  support  the  view  that  intestinal  flagellates  are  of 
more  importance  pathogenically  than  has  commonly  been  sup- 


PATHOGENIC  IMPORTANCE 


117 


posed  have  been  furnished  recently  by  the  findings  in  returned 
British  soldiers,  in  whom  uncomphcated  infections  with  flagel- 
lates have  been  found  in  many  dysenteric  cases,  and  also  by  the 
investigations  of  Lynch,  Barlow,  Escomel  and  others  in  various 
parts  of  the  world.  Still  further  evidence  is  furnished  by  the 
fact  that  parasites  very  closely  allied  to  species  found  in  man 
have  recently  been  shown  to  be  unquestionably  of  pathogenic 
importance,  at  least  under  certain  conditions,  in  lower  animals. 

Obviously,  however,  in  view  of  the  large  number  of  infected 
persons,  the  intestinal  protozoans  must  often  have  little  or  no 
pathogenic  effect.  There  is,  nevertheless,  much  individual  dif- 
ference in  susceptibility,  and  different  strains  of  the  same  para- 
site seem  to  vary  in  the  effects  they  produce.  Moreover  it  is 
highly  probable  that  a  great  many  slight  and  perhaps  almost 
unnoticed  symptoms,  resulting  in  a  certain  amount  of  interference 
with  the  digestive  tract  and  in  a  general  lowering  of  the  health, 
may  find  their  ultimate  cause  in  intestinal  parasites,  either  pro- 
tozoans or  worms  or  both.  The  health  of  people  living  in  warm 
and  tropical  countries,  even  aside  from  the  effects  of  malaria  and 
other  warm-climate  diseases,  is  proverbially  less  perfect  than  that 
of  people  in  the  usually  more  sanitary  northern  countries.  It  is 
quite  probable  that  intestinal  Protozoa  may  play  a  part  in  this 
lowering  of  the  tone  of  health. 

In  the  paragraphs  below  a  brief  account  of  the  more  important 
intestinal  flagellates  and  ciliates  is  given,  with  what  is  known  of 
their  pathogenic  effects,  in  the  following  order:  (1)  the  bi-flagel- 
late  forms,  Bodo,  Cercomonas  and  Embadomo7ias,  (2)  the  multi- 
flagellate  forms,  Trichomonas,  Enteromonas,  Chilomastix  and 
Giardia;  and  (3)  the  ciliate,  Balantidium. 


Bi-flagellate  Protozoa 

Most  primitive  of  the  intestinal  flagellates  are  the  bi-flagel- 
lated  forms,  several  genera  of  which  have  been  found  in  the  human 
intestine.  The  relation  of  these  animals  to  the  still  more  primi- 
tive mono-flagellated  trypanosomes  and  their  allies  is  shown 
by  the  parasites  of  the  genus  Trypanoplasma.  The  animals  of 
this  genus  resemble  trypanosomes  in  the  general  form  of  the  body 
and  in  the  possession  of  a  parabasal  body  and  an  undulating 
membrane,  but  have  an  additional  free  flagellum.     In  Cercomonas 


118  INTESTINAL  FLAGELLATES  AND  CILIATES 

(Fig.  29C),  according  to  Wenyon,  the  trailing  flagellum  is  at- 
tached to  the  side  of  the  body  as  far  as  the  posterior  end,  usually 
being  continued  as  a  free  flagellum.  According  to  others  Cer- 
comonas  has  only  a  single  flagellum,  the  free  one  at  the  anterior 
end.     Bodo  (Fig.  29B)  has  two  free  flagella,  one  waving  anteriorly, 


Fig.  29.  Bi-flagellated  parasites  A,  Prowazekella,  separation  from  Bodo 
proposed  on  account  of  absence  of  parabasal  body.  B,  Bodo,  note  parabasal  body 
(par.  b.).  C,  Cercomonas;  note  trailing  flagellum  attached  to  side  of  body.  This 
is  not  recognized  as  a  flagellum  by  some  workers.     X  2000.     (After  Wenyon.) 

the  other  trailing  behind;  some  species  not  showing  a  parabasal 
body  have  been  placed  in  a  genus  Prowazekella  (Fig.  29A)  of 
doubtful  validity.  Most  of  these  flagellates  are  coprozoic,  i.e., 
saprophytic  faecal  protozoa,  rather  than  true  parasites,  the  cysts 
being  accidentally  ingested  with  water  or  food. 

A  slipper-shaped  flagellate,  Emhadomonas  (Waskia)  intestinalis, 
first  described  by  Wenyon  and  O'Connor  in  Egypt,  and  since 
recorded  by  Kofoid,  Kornhauser  and  Plate  in  American  troops 
returning  from  overseas,  and  by  Hogue  from  a  person  who  had 
never  been  out  of  the  United  States,  is  probably  a  true  human 
intestinal  parasite.  It  is  only  from  4  to  8  /^  in  length,  has  a  rather 
large  cytostome,  an  anterior  nucleus,  and  two  flagella,  one  of 
which  is  short  and  thick  and  lies  in  the  cytostome.  The  cysts 
are  very  small  and  pear-shaped.  A  larger  species,  Emhado- 
monas sinensis  has  been  found  by  Faust  in  China. 

Multi-fiagellate  Intestinal  Protozoa 

Trichomonas  hominis,  —  Of  the  several  flagellates  which 
have  been  found  in  the  human  digestive  tract  and  faeces.  Tricho- 
monas is  the   commonest.      It  makes  its   home  in   the   upper 


TRICHOMONAS 


119 


c>t.— -V 


par.b.m 


part  of  the  large  intestine  and  coecum,  often  multiplying  in 
prodigious  numbers.  Trichomonas  also  lives  in  the  vagina  and 
in  the  urinary  tract,  being  quite  often  found  in  vaginal  discharges, 
especially  in  cases  of  leucorrhea.  It  has  been  commonly  believed 
that  the  vaginal  parasite,  which  is  larger  than  that  of  the  intestine, 
is  a  distinct  species,  and  it  has  been  given  the  name  T.  vaginalis^ 
but  there  is  reason  for  believing  that  it  is  identical  with  the  in- 
testinal parasite.  Other  intestinal  parasites  are  sometimes 
found  in  the  urinary  tract.  This  or  a  closely  allied  species  is  also 
occasionally  found  in  the  mouth, 
about  the  tartar  of  the  teeth.  Ac- 
cording to  Goodey  the  mouth  form 
differs  from  the  intestinal  form  to 
a  sufficient  extent  to  warrant  its 
being  given  a  distinct  name,  at  least 
provisionally,  and  he  proposes  the 
name  Trichomonas  ( Tetratrichomo- 
nas)  buccalis. 

Trichomonas  hominis  (Fig.  30) 
is  a  pear-shaped  flagellate  averaging 
about  eight  to  15  ^u  (^tjVit  to  j-^  of 
an  inch)  in  length,  the  size  being  in- 
versely proportional  to  the  rapidity 
of  multiplication.  Typically  it  has 
three  vigorously  moving  anterior 
flagella  arising  from  the  blunt  an- 
terior end,  and  a  fourth  wavy  one 
which  turns  backward  and  is  at- 
tached to  the  side  of  the  body  by 
an  undulating  membrane.  Some 
investigators  however,  record  four  free  flagella  and  others  five. 
On  this  basis  new  species  and  genera  have  been  created  but,  as 
pointed  out  by  Faust,  it  is  more  probable  that  all  of  them  may  be 
included  under  a  single  species,  with  races  among  which  the 
number  of  flagella  may  vary,  but  within  any  one  of  which  it  tends 
to  remain  constant,  usually  either  three  or  four.  Goodey  de- 
scribes the  mouth  form  of  the  parasite  as  having  four  flagella. 
Along  the  line  of  attachment  of  the  undulating  membrane  to  the 
body  is  a  structure  which  takes  a  deep  stain,  called  the  chro- 
matic basal  rod  or  "  costa."     It  is  beheved  by  some  workers  to 


axo. 


Fig.  30.  Trichomonas  hominis; 
n.,  nucleus;  cyt.,  cytostome;  axo., 
axostyle;  par.  b.,  parabasal  body 
(?) ;  und.  m.,  undulating  membrane. 
X  2400.     (After  Wenyon.) 


120  INTESTINAL  FLAGELLATES  AND  CILIATES 

be  a  modified  parabasal  body;  in  some  forms  it  is  broken  up  into 
a  row  of  chromatinic  granules.  At  the  point  of  insertion  of  the 
flagella,  and  serving  as  the  center  of  the  neuromotor  apparatus  is 
a  basal  granule  or  blepharoplast.  Arising  near  the  anterior  end 
and  running  through  the  body  is  a  sort  of  supporting  rod  called  the 
"  axostyle,"  which,  according  to  Kofoid  and  Swezy,  is  also  used 
as  an  organ  of  locomotion.  At  the  anterior  end  at  one  side  of 
the  point  where  the  flagella  originate  is  a  slight  depression  or 
"  cytostome  "  which  serves  as  a  mouth.  The  small  round  nu- 
cleus lies  in  the  body  just  behind  the  origin  of  the  flagella. 

Trichomonas  swims  by  active  lashing  movements  of  the  free 
flagella  and  by  wave  motions  of  the  undulating  membrane. 
The  body  revolves  as  the  animal  wends  its  way  through  the 
semi-hquid  substances  in  which  it  lives.  Multiplication  is  by 
longitudinal  division  of  the  body,  the  flagella  and  undulating 
membranes  and  internal  structures  all  being  duplicated  before 
the  animal  splits  into  two.  A  process  of  multiple  fission  resulting 
in  the  formation  of  eight  individuals  has  also  been  described. 

Encystment,  such  as  occurs  in  other  intestinal  protozoans, 
has  definitely  been  observed  only  recently  in  Trichomonas. 
Some  of  the  flagellates,  after  escaping  from  the  body  with  the 
fseces,  soon  degenerate,  gradually  losing  all  their  appendages 
except  the  undulating  membrane.  With- 
out their  flagella,  and  with  their  ameboid 
movements,  these  animals  closely  resemble 
amebse  but  can  usually  be  identified  by  the 
undulating  movement  which  persists  at  one 
side  of  the  body.  Others,  without  losing 
inJe^ruiiisi  A^^rtZcyZ  ^^^^^  appendages,  become  round  and  mo- 
ment stage;  B,  encysted  tionless  as  if  in  a  cyst,  but  with  no  cyst 
Lynch.)  ^  •  (  ter  ^^jj  around  them.  When  warmed  up 
they  stretch  themselves  out  and  resume 
an  active  life.  It  is  probable  that  these  forms  are  preparing  for 
encystment,  since  they  correspond  with  pre-encystment  forms 
(Fig.  31  A)  recently  described  by  Lynch.  Lynch,  who  found  con- 
siderable numbers  of  cysts  in  a  heavily  infected  case  in  South 
Carolina,  describes  the  cysts  (Fig.  31B)  as  thin-shelled,  pear- 
shaped  bodies,  about  three-fourths  the  size  of  the  active  flagellates. 
The  oval  body  of  the  animal  with  its  appendages  can  be  seen 
clearly  through  the  cyst  wall  in  properly  prepared  microscopic 


PATHOGENICITY  OF  TRICHOMANAS  121 

slides.  It  is  the  opinion  of  many  protozoologists,  however,  that 
these  so-called  cysts  are  really  degenerate  forms,  and  that  cyst 
formation  has  not  yet  been  satisfactorily  demonstrated.  Lynch 
and  others  have  succeeded  in  cultivating  Trichomonas  and  in 
infecting  rabbits  with  it,  but  specimens  cannot  be  kept  alive  in 
water  or  f seces  for  more  than  a  few  days  under  the  most  favorable 
conditions. 

Trichomonas  is  generally  regarded  as  a  harmless  parasite,  but 
there  seems  to  be  strong  evidence  that  it  often  causes  diarrhea, 
sometimes  very  severe  and  of  long  duration.  Epidemics  of 
diarrhea  and  mild  dysenteric  symptoms  in  man  apparently  caused 
by  Trichomonas  have  been  reported  from  Peru,  Brazil,  China, 
South  Carolina  and  Indiana,  and  it  is  probable  that  the  parasite 
is  at  least  mildly  pathogenic  wherever  it  occurs,  tending  to  ag- 
gravate other  intestinal  ailments  if  not  causing  them  directly. 
Haughwout  suggests  the  following  possible  ways  in  which  this 
parasite  may  damage  its  host:  (1)  production  of  growth-inhibiting 
substances;  (2)  production  of  substances  directly  toxic;  (3) 
liberation  of  injurious  metabolic  products;  (4)  mechanical  ir- 
ritation of  mucous  membranes;  (5)  interference  with  absorption 
by  adherence  to  intestinal  walls;  (6)  invasion  and  destruction  of 
tissues.  On  the  other  hand  Wenyon  and  O'Connor  regard  the 
presence  of  Trichomonas  in  cases  of  diarrhea  as  usually  accidental, 
and  fixed  upon  as  the  cause  because  the  most  conspicuous  or- 
ganism present.  A  case  has  recently  been  reported  of  an  Oriental 
who  was  suffering  from  a  foul-smelling  decay  of  the  jaw,  accom- 
panied by  pains  in  the  joints,  in  which  numerous  Trichomonas 
were  found  in  the  jaw  lesion.  After  treatment  with  emetin  there 
was  rapid  improvement,  which  suggests  that  Endamoeha  may 
also  have  been  present. 

No  specific  drug  for  use  against  Trichomonas  has  yet  been 
found.  Methylene  blue  in  weak  solutions  is  absorbed  by  the 
parasites  and  causes  them  to  become  round  and  quiet.  Castellani 
recommends  taking  methylene  blue  both  by  mouth  and  by  means 
of  an  enema,  i.e.^  irrigation  of  the  large  intestine.  With  this 
treatment  the  flagellates  are  said  to  decrease  rapidly  and  to  disap- 
pear usually  within  a  few  days.  Escomel,  who  has  found  Tri- 
chomonas an  important  factor  in  diarrhea  in  Peru,  advises  an 
enema  consisting  of  one  grain  of  iodine  in  a  liter  of  water,  taken 
in  the  evening  on  three  successful  days.     Unless  the  parasites 


122 


INTESTINAL  FLAGELLATES  AND   CILIATES 


have  established  themselves  in  the  membranes  high  up  in  the 
intestine  they  are  said  to  disappear  after  this  treatment.  As 
with  other  intestinal  Protozoa  infection  occurs  through  polluted 
food  or  water. 

Enteromonas  hominis.  —  This  minute  spherical  or  nearly- 
spherical  organism,  5  to  6  /z  in  diameter,  was  first  described  by 
Fonseca  in  Brazil.  It  possesses  two  equal  anterior  flagella,  and 
a  larger  trailing  flagellum ;  the  nucleus  is  situated  anteriorly  as  in 
Chilomastix.  It  is  probable  that  Tricercomonas  and  Diplocerco- 
monas,  described  as  distinct  human  parasites,  are  really  identical 
with  Enteromonas. 

Chilomastix  {or  Macrostoma)  mesnili,  —  A  parasite  which 
closely  resembles  Trichomonas  in  many  respects  is  Chilomastix 


Fig.  32.  Chilomastix  (or  Macrostoma)  mesnili;  A,  adult  parasite (n.,  nucleus; 
cyt.,  cytostome,  4th  fl.,  fourth  flagellum) ;  B,  end  view  of  adult  parasite,  showing 
eytostome  with  flagellum  in  it;  C,  degenerating  form,  resembling  an  ameba;  D, 
cyst,  showing  nucleus  and  cytostome.     X  2000.  (After     Wenyon.) 

mesnili  (Fig.  32).  It  is  smaller  than  the  former,  averaging  about 
eight  or  ten  n  (^t^Vtt  of  an  inch)  in  length.  It  has  three  slender 
anterior  flagella  like  Trichomonas  but  has  no  conspicuous  undulat- 
ing membrane.  It  has  a  large  and  conspicuous  slit  or  cytostome 
along  one  side  which  corresponds  to  the  very  small  mouth  cavity 
of  Trichomonas.  Within  the  cytostome  is  a  fourth  inconspicu- 
ous flagellum  which  seems  to  be  attached  to  a  small  undulating 
membrane.  The  posterior  end  of  the  body  is  drawn  out  into  a 
long  point.  As  in  Trichomonas  the  nucleus  hes  just  behind  the 
origin  of  the  flagella.  The  rest  of  the  body  contains  numerous 
vacuoles  filled  with  bacteria,  the  latter  apparently  serving  as  the 
staple  article  of  diet. 


GIARDIA  INTESTINALIS  123 

The  ordinary  multiplication  of  Chilomastix  is  no  doubt  similar 
to  that  of  Trichomonas.  When  ready  to  leave  the  body  oval 
cysts  are  formed  from  7  to  8  m  (^/t)-?^  of  an  inch)  in  length, 
within  which  the  animal  with  its  nucleus  and  large  cytostome  can 
be  seen  (Fig.  32D).  Wenyon  has  found  Chilomastix  cysts  with 
four  nuclei  and  thinks  that  some  multiplication  may  occur 
within  the  cysts  as  it  does  in  Endamoeba.  The  methods  of  trans- 
mission and  means  of  prevention  differ  in  no  way  from  those 
of  Trichomonas. 

Giardia  (or  Lamhlia)  intestinalis,  —  Next  to  Trichomonas, 
Giardia  is  the  most  common  flagellate  in  the  human  digestive 
tract.  Unlike  most  of  the  other  intestinal  protozoans  it  estab- 
lishes itself  in  the  upper  part  of  the  small  intestine.  It  is  one 
of  the  oddest-shaped  little  animals  known.  Wenyon  aptly 
describes  it  as  follows:  *'  In  shape  it  resembles  a  pear  split  into 
two  parts  along  the  longitudinal  axis.  There  is  a  flat  surface 
on  which  there  is  a  sucking  disk  with  raised  edge,  and  a  convex 
surface.  The  tapering  extremity  or  tail  can  be  turned  over  the 
convex  back,  and  it  terminates  in  two  flagella.  There  are  three 
other  pairs  of  flagella,  the  arrangements  of  which  are  best  seen 
by  referring  to  the  plate."     (Fig.  33.) 

Giardia  is  remarkable  in  being  perfectly  bilaterally  symmetrical, 
every  organelle,  including  the  nucleus,  being  accurately  repro- 
duced on  each  side  of  the  middle  line.  Between  the  two  small 
nuclei  are  a  pair  of  rodlike  structures  (Fig.  33,  par.  b.)  thought  by 
some  workers  to  be  parabasal  bodies,  from  which  the  flagella 
arise.  As  seen  in  face  view  the  parasite  has  a  comical  owl-Hke 
appearance.  This  fantastic  little  animal,  12  to  18  /x  (^(jVt?  to  t^js 
of  an  inch)  in  length  fastens  itself  to  the  convex  surface  of  an 
epithelial  cell  by  means  of  its  sucking  disk,  resting  with  its 
flagella  streaming  like  the  barbels  of  a  catfish  (Fig.  33F).  Some- 
times long  rows  of  them  can  be  found  resting  on  the  surface  of  the 
epithelial  cells  of  digestive  glands.  Miss  Porter,  who  has  studied 
Giardia  infections  in  British  soldiers  from  Gallipoli,  estimated 
recently  that  in  one  case  the  number  of  cysts,  each  having  been 
an  active  flagellate  in  the  intestine,  exceeded  14,000,000,000  in 
a  single  stool.  The  number  of  cysts  in  an  average  stool  in  a 
case  of  moderate  infection  she  estimated  at  324,000,000. 

Evidently  this  flagellate  multiplies  very  rapidly,  but  its  method 
of  multiplication  is  not  fully  understood.     Division  of  unen- 


124 


INTESTINAL  FLAGELLATES  AND  CILIATES 


cysted  forms  has  very  rarely  been  observed,  and  some  writers 
have  even  gone  so  far  as  to  say  that  it  does  not  occur.  It  is  well 
known  that  division  into  two  individuals  takes  place  after  en- 
cystment,  and  Wenyon  has  recently  expressed  the  opinion  that 
if  the  division  is  completed  before  the  cyst  is  expelled  from  the 
body  of  the  host,  the  cyst  may  burst  and  liberate  the  two  animals, 


Fig.  33.  Giardia  (or  Lamblia)  intestinalis;  A,  side  view  (s.  sucker-like  depres- 
sion); B,  ventral  view  (par.  b.,  parabasal  bodies,  n.,  nucleus);  C,  young  cyst  with 
four  nuclei;  Z>,  mature  cyst  containing  two  parasites;  E,  end  view  of  young  cyst; 
F,  parasite  resting  on  epithelial  cell.  Figs.  A-E,  X  2Q00,  after  Wenyon;  Fig.  F, 
X  1000,  after  Grassi  and  Schewiakoff. 


the  cysts  thus  serving  as  a  means  of  multiplication.  Kofoid 
and  Christiansen  have  recently  succeeded  in  finding  numerous 
individuals  of  an  allied  parasite  of  the  mouse,  Giardia  muris, 
in  process  of  division  into  two  and  also  into  four  and  eight  indi- 
viduals, both  in  the  free  and  in  the  encysted  state.  That  a  simi- 
lar process  really  occurs  in  the  human  parasite  can  hardly  be 
doubted,  both  from  its  similarity  to  the  mouse  parasite  and  from 
the  enormous  numbers  which  may  occur  in  an  infected  person 
at  one  time. 

The  free  active  parasites  become  motionless  and  die  soon  after 
leaving  the  body  of  the  host  with  the  faeces,  but  encysted  forms 
(Fig.  33C,  D  and  E)  may  retain  their  vitality  for  a  very  long  time. 


GIARDIA  INTESTINALIS  125 

The  cysts  usually  form  around  single  animals  which  then  proceed 
to  divide  into  two  or  more  individuals.  The  commonest  condi- 
tion is  that  of  two  parasites  lying  with  their  anterior  ends  at 
opposite  ends  of  the  cyst  (Fig.  33D). 

According  to  Wenyon,  Giardia  is  a  very  persistent  flagellate, 
often  keeping  an  individual  infected  for  years.  It  is  sometimes 
noticeably  pathogenic,  causing  intermittent  diarrhea  in  which 
blood  and  mucus  is  passed,  swarming  with  parasites.  Between 
such  attacks  the  infected  person  passes  apparently  normal  stools, 
with  only  the  cysts  of  Giardia  in  them.  An  active  increase  of 
parasites  accompanied  by  attacks  of  diarrhea  is  likely  to  occur 
after  exposure  to  weather,  irregular  diet,  or  other  weakening 
conditions.  Many  cases  of  dysentery  and  diarrhea  in  British 
soldiers  invalided  home  from  Gallipoli  were  found  to  be  due  to 
Giardia  infection.  The  acute  symptoms  last  from  one  to  six 
months,  after  which  the  symptoms  practically  disappear  for  a 
variable  length  of  time.  Strangely  enough  there  is  always 
spontaneous  improvement  upon  a  change  to  a  cooler  cHmate. 

Giardia  infections  are  extremely  difficult  to  get  rid  of,  and 
some  infections  seem  to  survive  every  attempt  at  treatment. 
They  do  not  respond  to  emetin,  though  they  are  sometimes 
destroyed  by  beta-naphthol.  The  latter  drug  in  combination 
with  bismuth  saUcylate  has  been  found  successful  in  some  cases. 
Escomel  in  Peru  uses  a  method  of  dieting  followed  by  calomel 
and  castor  oil  and  claims  to  rid  his  patients  of  the  parasite  by  the 
third  day.  The  difficulty  experienced  in  expelling  these  para- 
sites is  probably  due  to  their  habit  of  lodging  themselves  in  the 
digestive  glands  outside  the  main  passage  of  the  intestine,  where 
it  is  difficult  for  drugs  of  any  kind  to  reach  them. 

Like  other  intestinal  protozoans,  Giardia  is  transmitted  in  the 
encysted  state  with  polluted  food  and  water.  Stiles  has  shown 
that  flies  play  an  important  role,  carrying  the  cysts  on  their  feet 
from  open  privies  and  depositing  them  on  human  food.  By  cap- 
turing flies  known  to  have  fed  on  Giardia-iniected  material  and 
shaking  them  up  in  distilled  water,  Stiles  was  able  to  recover 
Giardia  cysts  from  them. 

Deschiens  has  recently  adduced  strong  evidence  by  experimental 
infections  that  the  Giardia  of  rats  and  mice  is  really  only  a  variety 
of  the  human  species,  in  which  case  the  faeces  of  the  rodents 
would  afford  a  means  of  dispersal.  Cats  also  may  serve  as  a 
reservoir  and  means  of  dissemination  for  the  infection. 


126 


INTESTINAL  FLAGELLATES  AND  CILIATES 


Ciliates 

Balantidium  coli.  — Although  several  species  of  ciliates  have 
been  recorded  as  human  parasites,  there  is  only  one  species, 
Balantidium  coli  (Fig.  34A),  normally  parasitic  in  hogs,  which  is 
common  enough  to  be  of  any  importance.  This  large  ciliate 
stands  next  to  Endamoeba  histolytica  among  the  Protozoa  as  a 


Fig.  34.  Balantidium  coli;  A,  free  ciliate  from  intestine;  n.,  nucleus;  c.  v., 
contractile  vacuoles;  f.  v.,  food  vacuole;  cyt.,  cytostome.  B,  cyst,  as  passed  in 
faeces,  containing  two  parasites.      X  about  500.     (After  Wenyon.) 

cause  of  human  dysentery.  It  is  a  large  animal  for  a  protozoan, 
averaging  from  50  to  100  /*  (^^^  to  ^^^jj  of  an  inch)  in  length,  and 
thus  being  visible  to  the  naked  eye.  Its  body  is  oval  and  en- 
tirely covered  with  ciha,  and  at  the  anterior  end  there  is  a  gash- 
like slit  leading  to  the  mouth  or  "  cytostome  "  (Fig.  34,  cyt.). 
The  large  bean-shaped  nucleus  (Fig.  34,  n.)  lies  near  the  middle  of 
the  body  and  near  each  end  is  a  pulsating  cavity  or  contractile 
vacuole  (Fig.  34,  c.v.)  which  excretes  waste  matter.  These 
parasites  multiply  by  transverse  division,  often  so  rapidly  that 
the  animals  do  not  have  time  to  grow  to  full  size  and  so  become 
very  small.  When  ready  to  leave  the  body  they  form  an  oval 
cyst  about  themselves.  Sometimes  two  occupy  a  single  cyst 
(Fig.  34B),  and  later  fuse  together.  Since  the  ciUated  bodies  of 
the  protozoans  can  be  seen,  under  a  microscope,  inside  the  large 
transparent  cysts,  their  identification  is  not  difficult.  The  cysts 
can  exist  outside  the  body  for  a  long  time,  awaiting  an  opportunity 
for  reinfection. 


BALANTIDIUM   COLI  127 

Balantidium  swims  about  in  the  contents  of  the  large  intestine 
devouring  particles  of  faecal  material.  As  long  as  the  animal 
confines  its  activities  to  this,  no  ill  effects  result,  but  it  also  has 
the  power,  like  Endamoeba  histolytica,  of  invading  the  tissues 
and  causing  ulceration,  perhaps  after  an  injury  from  some  other 
cause  has  given  an  opening  for  invasion.  Although  many  in- 
fected persons  do  not  show  any  dysenteric  symptoms,  these  are 
likely  to  appear  at  any  time.  When  they  do  appear,  they  are 
of  a  very  serious  nature,  and  cause  a  high  mortality.  On  post 
mortem  examination  the  large  intestine  is  often  found  in  a  hor- 
rible condition,  ulcerated  from  end  to  end,  with  shreds  of  muti- 
lated or  dead  tissue  hanging  from  the  walls. 

Unfortunately  there  is  no  specific  treatment  for  balantidial 
dysentery  as  there  is  for  the  amebic  disease.  In  some  cases 
emetin  and  alcresta  ipecac  (see  p.  135)  have  caused  a  disap- 
pearance of  the  parasites,  but  these  are  not  reliable  remedies. 
Salvarsan  and  methylene  blue  have  also  been  recorded  as  suc- 
cessful in  some  cases.  Organic  compounds  of  silver  seem  to 
have  some  value  in  destroying  Balantidium,  and  there  are  other 
drugs  and  herbs  of  much  local  fame  which  are  undoubtedly 
sometimes  effective.  Rest  and  care  of  the  general  health  are 
always  required. 

Prevention  of  balantidial  dysentery  consists  not  only  in  the 
sanitary  disposal  of  human  faeces,  as  in  the  case  of  other  human 
intestinal  protozoans,  but  also  in  the  proper  care  of  hogs,  since 
Balantidium  is  a  common  parasite  of  these  animals,  and  is 
probably  norrrially  a  hog  parasite.  A  large  proportion  of  hogs 
are  infected  in  almost  all  warm  and  temperate  countries,  and  it  is 
nearly  always  in  hog-raising  countries,  and  in  places  where  there 
is  too  close  association  between  hogs  and  man,  that  balantidial 
dysentery  occurs.  Around  Manila,  where  the  disease  is  fairly 
common,  the  majority  of  the  hogs  are  infected  and  pass  encysted 
parasites  in  their  faeces  almost  constantly.  In  Colombia  the 
disease  is  found  only  in  those  altitudes  where  hogs  are  raised 
and  among  those  who  raise  them. 


CHAPTER  VIII 
AMEB^ 

Those  of  us  who  have  had  an  opportunity,  in  studying  micro- 
scopic life  in  water,  to  observe  the  restless  movements  of  the 
tiny  bits  of  naked  protoplasm  which  we  call  amebae,  having 
watched  them  slowly  creep  along  the  surface  of  a  slide,  extending 
a  portion  of  the  body  as  a  finger-like  projection  or  ''  pseudo- 
podium  "  and  then  allowing  the  rest  of  the  body  to  flow  up  to 
the  new  position;  having  seen  them  creep  up  on  tiny  protozoans 
or  other  single-celled  organisms  and  devour  them  by  merely 
wrapping  themselves  around  them,  thus  engulfing  them  in  an 
improvised  stomach;  and  having  seen  them  propagate  their 
kind  by  simply  constricting  in  the  middle  and  dividing  in  two; 
—  those  of  us  who  have  observed  these  acts  on  the  part  of  such 
tiny  and  simple  animals  have  come  to  be  fascinated  by  them  and 
to  like  them,  and  find  it  hard  to  realize  that  certain  species  are 
'nstrumental  in  causing  some  important  human  diseases.  Amebae 
are  found  almost  everywhere  in  water,  soil  and  carrion.  They 
have  even  been  found  recently  to  exist  in  large  numbers  in  the 
sunbaked  sands  of  the  Egyptian  deserts,  lying  dormant  in  their 
cysts  which  protect  them  from  evaporation,  ready  to  emerge 
and  resume  an  active  life  when  they  become  moistened.  In 
view  of  the  wide  adaptability  of  these  animals  it  is  not  surprising 
to  discover  some  living  as  parasites,  finding  congenial  surround- 
ings in  the  bodies  of  higher  animals. 

Classification.  —  Amebae  are  protozoans  belonging  to  the  sub- 
class Sarcodina,  a  group  characterized  by  a  body  without  a 
cuticle,  though  sometimes  protected  by  a  shell  or  cyst  wall,  and 
by  their  peculiar  method  of  locomotion.  In  the  adult  form  they 
have  neither  flagella  nor  cilia,  but  simply  outgrowths  of  proto- 
plasm, called  pseudopodia.  In  the  amebae  and  their  close  rela- 
tives the  pseudopodia  can  be  projected  anywhere  on  the  surface 
of  the  body,  now  here,  now  there,  though  the  number,  form  and 
activity  of  the  pseudopodia  are  quite  different  in  different  species. 

128 


PARASITIC  SARCODINA  129 

The  life  history  also  varies  in  the  different  species,  many  free- 
living  forms  possessing  a  flagellated  stage.  On  the  basis  of  struc- 
ture, life  history,  and  habits  the  old  genus  Amoeba  has  been  broken 
into  a  number  of  genera  distinguishable  from  each  other  prin- 
cipally by  the  structure  of  the  nucleus  and  the  nature  of  the  cysts. 
The  life  history  is  simple  in  all  of  them,  so  far  as  it  is  known.  The 
cases  of  spore  formation,  multiple  fission,  conjugation  or  sexual 
processes  described  by  various  investigators  have  not  been  sub- 
stantiated by  subsequent  work.  All  of  the  parasitic  amebae  are 
characterized  by  the  absence  of  contractile  vacuoles.  One  species, 
Endamoeba  histolytica,  habitually  feeds  on  blood  corpuscles  and 
living  tissues,  and  another,  Councilmania  lafleuri,  does  so  to  some 
extent.  The  other  species  apparently  feed  principally  on  bacteria 
and  other  organic  material  with  which  they  are  associated  in  their 
normal  habitat. 

The  principal  amebae  occurring  in  human  beings  may  be  ten- 
tatively grouped  in  the  five  genera  Endamoeba,  Councilmania, 
Endolimax,  lodamoeba,  and  Dientamoeba,  but  the  classification 
of  the  parasitic  amebae  cannot  yet  be  considered  as  satisfactorily 
settled.     The  characteristics  of  these  genera  are  briefly  as  follows : 

Endamoeba;  nucleus  vesicular  with  chromatin  arranged  in  a 
peripheral  layer  of  beadlike  granules  of  fairly  uniform  size,  and  a 
small  compact  karyosome;  a  capsule-like  structure  can  usually 
be  seen  surrounding  the  karyosome.  Cysts,  if  produced,  with 
normally  4  or  8  nuclei  of  similar  structure  to  those  of  the  free 
forms,  and  including  also  glycogen  masses  and  refractile  ''  chro- 
matoid "  bodies,  though  these  masses  and  bodies  commonly 
disappear  before  or  soon  after  the  cysts  become  mature.  (See 
Figs.  36  and  37.) 

Councilmania;  nucleus  with  chromatin  distributed  in  a  peri- 
pheral zone  on  nuclear  membrane  and  in  an  irregular  karyosome. 
Cysts  normally  with  8  nuclei  which  have  relatively  large  and  very 
variable  karyosomes,  and  very  little  peripheral  chromatin.  Buds 
containing  single  nuclei  escape  from  a  pore  in  the  cyst  wall  until 
the  cyst  is  emptied  of  all  its  nuclei.     (See  Fig.  41.) 

Endolimax;  nucleus  vesicular  without  a  distinct  peripheral 
layer  of  chromatin.  A  fairly  large  compact  mass  of  chromatin 
(karyosome)  in  the  interior,  usually  more  or  less  eccentric  and 
connected  by  threads  or  processes  with  one  or  more  smaller  masses. 
Mature  cysts  oval,  with  four  nuclei  in  the  single  known  species, 
similar  in  structure  to  those  of  the  free  forms.     The  cysts  contain, 


130 


AMEB^ 


^  n. 


Fig.  36.  Endamoeba  histolytica.  X  1650.  A,  stained  vegetative  ameba; 
B,  cyst  with  four  nuclei;  n.,  nucleus,  showing  peripheral  chromatin  granules  and 
central  karyosome;  r.  b.  c,  ingested  red  blood  corpuscles;  chr.  b.,  chromatoid 
body.     (After  Dobell.) 


Fig.  37.  Endamoeba  coli.  X  1650.  A,  stained  vegetative  ameba;  B,  cyst, 
with  eight  nuclei;  n.,  nucleus,  showing  coarse  peripheral  chromatin  granules, 
chromatin  granules  in  "clear  zone"  between  periphery  and  karyosome,  and 
eccentric  karyosome;  chr.  b.,  remnant  of  chromatoid  body.  Note  large  number 
of  food  vacuoles  in  vegetative  ameba.     (After  Dobell.) 


Fig.  38.  Endolimax  nana.  X  1650.  A,  two  stained  vegetative  forms,  show- 
ing nuclei  with  large  irregular  karyosome,  and  numerous  food  vacuoles.  B,  cyst 
with  four  nuclei.     (After  Dobell.) 


INTESTINAL  AMEB^ 


131 


^l.m.^- 


Fia.  39.  lodamoeba  butschlii.  X  1650.  A,  stained  vegetative  ameba,  showing 
numerous  food  vacuoles  and  nucleus  (n.),  the  latter  with  large  central  karyosome 
and  a  single  layer  of  granules  between  karyosome  and  nuclear  membrane.  B, 
cyst,  showing  nucleus  (n.)  with  peripheral  karyosome,  and  glycogen  mass  (gl.  m.) 
or  "iodophilic  body,"  from  which  these  cysts  received  the  name  "Iodine  or  I. 
cysts."     (After  Dobell.) 


Fio.  40.  Dientamoeba  fragilis.  X  1650.  A,  stained  vegetative  ameba,  show- 
ing two  nuclei  with  granular  karyosomes,  and  tood  vacuoles;  B,  living  ameba, 
showing  leaf -like  pseudopodia.     (A,  after  Dobell;   B,  after  Jepps  and  Dobeli.) 


Fig.  41.  Councilmania  lafteuri.  X  1650.  A,  stained  vegetative  ameba  with 
a  pseudopodium  in  early  phase  of  protrusion  and  one  nearly  retracted  and  filled 
with  endoplasm;  nucleus  showing  peripheral  chromatin  and  large  irregular,  ec- 
centric karyosome;  endoplasm  filled  with  food  vacuoles.  B,  cyst  showing  8 
nuclei,  thick  wall,  and  chromaphile  ridge  (dark)  nearly  encircling  body,  and  chro- 
matoid  bodies  in  form  of  scattered  threads.  C,  cyst  showing  bud  escaping  with 
one  nucleus;  large  chromatoid  body  in  center  of  cyst.     (After  Kofoid  and  Swezy.) 


132  AMEB^ 

in  addition  to  the  nuclei,  a  number  of  small  refractile  granules 
of  a  substance  known  as  volutin.  The  young  cysts  also  contain 
masses  of  glycogen.     (See  Fig.  38.) 

lodamoeba.  —  Nucleus  vesicular  with  moderate-sized  central 
karyosome  and  well  developed  membrane  without  a  distinct 
peripheral  zone  of  chromatin,  but  with  a  single  layer  of  rather 
large  granules  between  the  karyosome  and  the  outer  membrane; 
cysts  very  characteristic,  formerly  known  as  Iodine  cysts  or  I. 
cysts,  of  very  irregular  shape,  containing,  besides  a  single  nucleus, 
a  number  of  brightly  refractile  granules  and  a  relatively  large 
clearly  defined  solid  mass  of  glycogen  which  stains  very  deeply 
in  iodine.  The  nucleus  is  peculiar  in  that  the  karyosome  comes 
to  lie  peripherally  in  contact  with  the  nuclear  membrane.  (See 
Fig.  39.) 

Dientamoehci.  —  Mature  individuals  with  two  similar  nuclei; 
these  are  vesicular  with  a  large  central  karyosome  consisting  of 
a  number  of  granules;  nuclear  membrane  very  delicate  without 
distinct  peripheral  chromatin;   cysts  not  found.     (See  Fig.  40.) 

Intestinal  Amebae 

The  intestinal  amebae  of  man,  according  to  Dobell,  consist 
of  Endamoeha  histolytica,  E.  coli,  Endolimax  nana,  lodamoeha 
hutschlii  :.nd  Dientamoeha  fragilis,  and  to  these  must  be  added 
Councilmania  lafleuri  recently  described  by  Kofoid  and  Swezy. 
A  number  of  other  species  have  been  described  by  various  writers, 
but  these  have  probably  been  either  deteriorated  examples  of  the 
known  species,  body  cells  mistaken  for  amebae,  or  a  confusion  of 
two  other  organisms.  The  discovery  by  Craig  of  an  intestinal 
ameba  having  a  flagellated  stage,  and  now  known  as  Craigia  hom- 
iniSj  and  the  discovery  of  an  allied  species,  Craigia  migrans,  by 
Barlow,  have  not  been  corroborated  by  other  workers,  and,  as 
Dobell  has  pointed  out,  these  organisms  are  probably  in  reality  a 
mixture  of  known  amebae  and  flagellates.  A  number  of  species  of 
free-living  amebae  are  occasionally  found  in  faeces  of  human  beings, 
apparently  being  able  to  pass  through  the  digestive  tract  uninjured, 
but  unable  to  thrive  there.  These  amebae  are  usually  placed  in  the 
genus  Vahlkampfia,  in  which  there  is  not  a  flagellated  stage  in  the 
development.  Another  species  of  Sarcodina  occasionally  found 
in  human  faeces  is  Chlamydophrys  stercorea.     This  is  a  common 


ENDAMCEBA  HISTOLYTICA  133 

organism  in  the  faeces  of  various  animals  and  in  sewage,  but  there 
is  no  reason  to  beheve  that  it  should  be  considered  a  human  para- 
site. 

Endamoeha  histolytica.  Endamoeba  histolytica,  (Figs.  35  and 
36)  the  dysentery  ameba,  is  a  large  and  active  species,  18  ^  to  40  /z 
iiiJi^  to  -^'Qj^  of  an  inch)  in  diameter,  the  majority  being  be- 
tween 20  ft  and  30  /x  in  diameter.  They  are  rather  transparent 
in  appearance,  with  blunt  pseudopodia,  and  when  perfectly  fresh 
from  the  intestine  creep  along  in  a  sluglike  manner.  After  they 
have  been  outside  the  body  for  a  short  time  they  remain  in  one 
place  and  throw  out  large  clear  pseudopodia  composed  of  ecto- 
plasm sharply  separated  from  the  endoplasm  (Fig.  35).  The 
nucleus  is  very  indistinct  and  usually  eccentric  in  position.  The 
most  characteristic  feature  of  the  living  ameba,  however,  is  the 
presence  ot  ingested  blood  corpuscles  and  tissue  cells.  Ordin- 
arily there  are  from  one  to  ten  of  these,  but  according  to  Dobell 
there  may  be  forty.  The  amebae  after  being  fixed  and  stained 
can  be  distinguished  from  the  closely  allied  E.  coli  by  the  nu- 
cleus. This  has  a  peripheral  layer  of  small  uniform  granules  of 
chromatin,  no  chromatin  in  the  clear  zone  between  this  layer 
and  the  karyosome,  and  a  small  centrally  placed  karyosome  sur- 
rounded by  an  indefinite  clear  halo.  (Fig.  36A.)  E.  coli  has 
a  thicker  layer  of  peripheral  chromatin,  a  number  of  chromatin 
granules  in  the  clear  zone,  and  a  larger  karyosome,  eccentric  in 
position,  with  a  more  distinct  "  halo  "  (Fig.  37A). 

There  are  two  stages  in  the  life  history  of  this  ameba,  the  vege- 
tative and  the  cystic.  As  long  as  conditions  in  the  intestine  are 
favorable  for  their  growth  and  development,  the  amebae  continue 
in  their  active  vegetative  condition,  multiplying  by  simple  divi- 
sion of  the  body  into  two.  When  conditions  have  become  unfavor- 
able for  them,  however,  as  in  later  stages  of  the  disease,  they 
decrease  in  size,  become  rounded,  and  begin  to  develop  a  cyst 
wall.  This  is  known  as  the  precystic  stage.  From  this  stage 
they  pass  rapidly  into  the  cystic  stage  by  the  completion  of  the 
cyst  wall  and  the  division  of  the  nucleus  into  four  daughter  nu- 
clei, thus  forming  the  well-known  "  tetragena  "  cysts,  long  sup- 
posed to  belong  to  a  distinct  species  (Fig.  36B).  The  size  of  the 
cysts  varies  from  5  jn  to  20  m  (zih-^  ^o  tAtt  o^  ^^  inch)  in 
diameter  and  there  are  a  number  of  races  or  varieties  of  the  ameba 
which  differ  from  each  other  in  the  average  size  of  the  cysts. 


134  AMEB^ 

The  nuclei  have  exactly  the  same  structure  as  in  the  free  amebse 
but  are  smaller.  The  majority  of  freshly  passed  cysts  contain 
blocks  or  masses  of  a  highly  refractile  substance,  called  chroma- 
toid  bodies  by  Dobell  (Fig.  36B,  Chr.  b.).  These  gradually  dis- 
appear in  the  course  of  a  few  days.  The  normal  cysts  of  the 
dysentery  ameba  are  distinguishable  from  those  of  E.  coli  by 
the  number  of  nuclei,  and  also  by  the  central  position  of  the 
karyosomes.  The  cysts  pass  out  with  the  fseces  of  the  infected 
individual,  and  live  outside  the  body  for  a  number  of  weeks  if 
kept  cool  and  moist.  They  are  destroyed  by  desiccation  and 
degenerate  rapidly  at  high  temperatures. 

As  cysts  the  amebae  are  dispersed  by  "  night  soil  "  when  used 
as  fertilizer,  by  seepage  into  water,  by  flies  and  other  insects, 
or  by  other  means.  If  by  any  of  these  means  they  reach  human 
food  or  water  and  thus  secure  entrance  to  the  digestive  tract, 
the  cyst  wall  is  dissolved  by  the  pancreatic  juice  and  four  little 
amebae,  each  containing  one  of  the  daughter  nuclei  which  were 
formed  when  the  cyst  first  developed,  are  set  free  in  the  intestine 
and  begin  to  grow  and  multiply.  The  active  vegetative  amebae 
from  an  acute  case  of  dysentery  are  destroyed  in  the  stomach  if 
swallowed,  and  only  the  parasites  in  the  encysted  stage,  with  an 
enclosing  capsule  to  protect  them  from  being  digested,  can  reach 
the  intestine  and  cause  disease. 

The  dysentery  amebae  inhabit  the  tissues  of  the  walls  of  the 
large  intestine,  where  they  cause  more  or  less  extensive  ulcer- 
ation. From  this  point  they  are  carried  by  the  lymph  or  blood 
stream  to  various  other  parts  of  the  body,  where  they  form 
local  abscesses.  Such  abscesses  are  commonest  in  the  liver  but 
occasionally  occur  in  other  organs,  such  as  the  lungs,  brain  and 
spleen.  The  amebae  probably  live  entirely  on  the  living  tissues 
and  blood  corpuscles,  the  tissues  being  destroyed  by  means  of  a 
powerful  cell-destroying  substance  produced  by  them. 

Until  recently  the  dysentery  ameba  was  thought  to  be  almost 
exclusively  a  parasite  of  tropical  and  subtropical  countries,  but 
in  recent  years  it  has  been  shown  to  be  widespread  throughout 
temperate  climates  as  well,  having  been  found  endemic  in  nearly 
all  parts  of  the  United  States  and  in  the  British  Isles  and  Central 
Europe.  The  amount  of  endemic  infection  in  temperate  parts 
of  both  Europe  and  America  has  been  greatly  increased  since  the 
European  war.     Kofoid  Kornhauser  and  Plate  found  10.8  per 


AMEBIC  DYSENTERY  135 

cent  infection  among  returned  American  overseas  troops  m  con- 
trast to  3  per  cent  in  home  service  troops.  In  India,  on  the  other 
hand,  MacAdam  estimates  that  one-third  of  the  inmates  of 
hospital  wards  are  infected  with  E.  histolytica. 

Amebic  Dysentery  and  Liver  Abscesses.  —  One  of  the  most 
serious  menaces  in  the  tropics  is  dysentery;  people  who  have 
always  lived  in  temperate  countries  have  no  conception  of  the  se- 
verity of  this  ailment.  In  many  tropical  countries  dysentery  ranks 
next  only  to  malaria  as  a  cause  of  death,  and  very  often  it  finishes 
the  work  of  such  diseases  as  malaria,  kala  azar  and  other  fevers. 
There  are  many  different  types  of  dysentery,  especially  in  the 
tropics,  each  showing  somewhat  different  symptoms  and  having 
to  be  treated  in  different  ways.  Some  cases  of  dysentery  are  due 
merely  to  improper  diet,  some  to  disturbances  of  the  digestive 
tract  due  to  other  diseases,  and  the  majority  to  intestinal  para- 
sites of  some  kind,  either  bacteria,  protozoans,  or  worms.  In 
a  restricted  sense  "  dysentery  "  is  used  for  intestinal  diseases 
caused  by  bacteria  or  protozoans.  The  diseases  caused  by  pro- 
tozoans other  than  amebse  are  discussed  in  the  chapter  preceding 
this.  "  Bacillary  dysentery  "  is  a  bacterial  disease  and  need  not 
be  discussed  here  except  in  comparison  with  other  types  of  dysen- 
tery. It  occurs  in  temperate  as  well  as  in  tropical  countries  and 
is  very  common  in  epidemic  form  in  armies,  prisons  and  asylums. 
Amebic  dysentery,  on  the  other  hand,  is  uncommon  outside  of 
warm  climates,  but  is  of  frequent  occurrence  in  local  areas  in  almost 
all  tropical  and  subtropical  countries,  where  frequently  a  large 
majority  of  dysentery  cases  are  caused  by  amebse.  The  propor- 
tion of  cases  of  amebic  dysentery  to  infections  with  the  amebae 
seems  to  be  higher,  and  the  disease  more  severe,  in  warm  than  in 
temperate  climates.  Many  of  the  cases  of  "  trench  diarrhea  " 
which  occurred  in  France  were  a  mild  form  of  amebic  dysentery. 

The  role  played  by  amebae  in  dysentery  was  in  doubt  for  a 
long  time.  The  presence  of  amebae  in  perfectly  healthy  individ- 
uals and  the  fact  that  amebae  grown  in  artificial  cultures  would 
never  give  rise  to  dysentery  experimentally  confused  the  problem. 
There  are  several  reasons  for  this  confusion.  In  the  first  place 
there  are  common  species  of  intestinal  amebae,  especially  Enda- 
moeha  coli  and  Endolimax  nana  which  do  not  attack  the  tissues 
or  cause  dysenteric  symptoms,  but  which  are  easily  confused 
with  E.  histolytica.     In  the  second  place,  non-parasitic  amebae 


136  AMEB.E 

normally  found  in  water  or  soil,  may  pass  through  the  intestine 
uninjured,  and  these  are  the  ones  which  have  commonly  been  ob- 
tained in  cultures  from  faeces.  In  the  third  place  infection  with 
Endamoeha  histolytica  does  not  by  any  means  cause  dysentery 
in  all  cases;  in  fact,  it  may  be  said  that  in  a  normal  infection 
there  is  sufficient  resistance  on  the  part  of  the  host  so  that  no 
appreciable  harm  results  from  the  attacks  of  the  parasites.  The 
injury  done  to  the  tissues  is  repaired  rapidly,  and  while  a  certain 
amount  of  ulceration  probably  exists  in  practically  all  cases, 
it  may  not  be  sufficient  to  cause  dysentery.  Individuals 
who  thus  harbor  amebae  without  being  greatly  inconvenienced 
by  them  are  the  so-called  "  carriers  "  of  the  disease.  It  is  prob- 
able that  only  a  small  percent  of  infections,  possibly  only  10  per 
cent,  actually  give  rise  to  dysenteric  symptoms.  The  carriers 
constitute  the  principal  means  of  dispersal  of  the  parasites,  since, 
to  protect  themselves  against  the  reactions  of  the  host,  the  amebse 
are  constantly  encysting,  and  the  cysts  are  constantly  being  lib- 
erated with  the  faeces.  In  acute  cases  only  free  amebse,  which 
cannot  infect  other  individuals,  are  passed;  convalescents,  how- 
ever, usually  become  carriers  for  variable  lengths  of  time,  and 
may  frequently  suffer  relapses. 

The  Disease.  —  Experiments  made  by  Walker  and  Sellards 
in  feeding  ameba-infected  material  to  animals  and  human  vol- 
unteers showed  that  dysenteric  symptoms,  if  they  appeared,  oc- 
curred in  from  20  to  94  days,  averaging  about  two  months.  The 
most  marked  symptom  is  an  acute  diarrhea  in  which  the  stools 
consist  largely  of  blood  and  mucus.  In  a  typical  case  from  Ala- 
bama a  patient  passed  as  many  as  fifteen  or  twenty  stools  in  an 
hour.  This  condition  had  been  going  on  for  years,  recurring 
about  three  or  four  times  a  year,  lasting  a  month  at  a  time.  In 
the  intervals  between  these  attacks  the  symptoms  were  mild  and 
the  patient  passed  only  two  or  three  stools  a  day.  Sometimes 
the  attacks  are  more  regularly  chronic,  or  may  recur  at  long  in- 
tervals. Often  the  dysentery  is  accompanied  by  evening  fever 
and  anemia  from  loss  of  blood  in  the  bowels. 

Instead  of  producing  ulcers  on  the  mucous  surface  of  the  large 
intestine  such  as  occur  in  bacillary  dysentery,  the  amebae  com- 
monly work  deeper  into  the  muscular  linings  of  the  intestines. 
Local  swellings  first  appear,  followed  by  an  ulceration  of  the 
mucous  membrane.     This  produces  a  portal  for  the  entrance  of 


TREATMENT  OF  AMEBIC  DYSENTERY  137 

the  amebae  to  the  tissue  underlying  the  mucous  membrane,  and 
here  they  make  extensive  excavations.  The  lesions  are  most 
common  in  the  upper  half  of  the  large  intestine  but  can  be  found 
from  the  lower  part  of  the  small  intestine  to  the  rectum.  The 
exposed  ulcerations  vary  from  the  size  of  a  pinhead  to  that  of  a 
silver  dollar,  their  ragged  edges  tending  to  roll  into  the  crater- 
like areas.  Often  the  tunnel-like  excavations  under  the  mucous 
membrane  connect  with  one  another. 

Liver  abscess  is  a  common  result  of  infection  with  Endamceba 
histolytica.  Often  these  abscesses  are  of  large  size,  filled  with  a 
slimy  and  somewhat  bloody  chocolate-colored  pus.  Over  a  quart 
of  such  pus  has  been  removed  from  an  amebic  liver  abscess. 
The  parasites  are  found  at  the  edges  of  the  abscess,  eroding  more 
tissue  and  enlarging  the  pus  cavity.  How  they  reach  the  liver 
to  do  their  damage  is  not  certainly  known,  but  it  seems  probable 
that  they  bore  into  blood  vessels  in  the  walls  of  the  diseased  large 
intestine  and  are  carried  by  the  portal  vein  to  the  liver,  where 
they  find  a  fertile  feeding  ground. 

Infections  with  E.  histolytica  are  very  persistent,  and,  with- 
out treatment,  may  persist  throughout  the  lifetime  of  the  host. 
In  many  cases  dysenteric  symptoms  never  develop,  while  in  other 
cases  there  may  be  intermittent  attacks  or  an  attack  after  the 
infection  has  persisted  harmlessly  for  months  or  years. 

Treatment  and  Prevention.  —  One  of  the  greatest  discoveries 
in  the  field  of  medical  treatment  since  the  production  of  salvar- 
san  by  Ehrlich  is  the  discovery  of  emetin  as  a  specific  against 
amebic  dysentery.  Emetin  is  an  alkaloid  prepared  from  ipecac, 
the  extract  of  the  roots  of  a  Brazilian  herb.  It  was  long  known 
that  ipecac  sometimes  had  a  very  marked  effect  on  dysentery, 
but  since  amebic  dysentery  has  only  recently  been  differentiated 
from  other  forms  very  variable  results  were  obtained  from  its  use. 
Ipecac  has  a  decided  disadvantage  in  that  it  causes  violent  vom- 
iting, but  its  alkaloid,  emetin,  in  the  form  of  emetin  hydrochloride, 
while  possessing  all  the  beneficial  properties  of  ipecac,  can  be  used 
in  the  form  of  injections  into  the  veins,  and  therefore  does  not 
cause  vomiting.  Experiments  with  cultural  species  of  amebae 
showed  that  emetin  (emetin  hydrochloride)  is  destructive  to 
amebae  when  diluted  500,000  times,  and  the  intestinal  amebae 
on  a  microscope  slide  become  round  and  motionless  and  appar- 
ently dead  when  subjected  to  this  very  dilute  solution.     It  is  now 


138  AMEByE 

thought  however,  that  emetin  acts  rather  by  its  effect  on  the  tissues 
of  the  host  than  by  its  direct  poisonous  action  on  the  amebae. 
Emetin  is  given  in  hypodermic  injections.  Almost  without 
exception  the  effect  of  the  drug  on  the  disease  is  certain  and  rapid. 
Severe  cases  which  have  been  running  on  for  years  can  be  cured 
in  four  or  five  days  by  this  simple  treatment.  One  of  the  chief 
disadvantages  is  that  the  treatment  is  often  discontinued  too 
soon.  The  dysenteric  symptoms  disappear  as  if  by  magic  and 
the  patient  is  often  not  willing  to  be  subjected  to  continued  drug 
injections  until  every  trace  of  the  amebae  has  disappeared. 
Emetin  is  powerless  against  encysted  amebae  and  an  apparently 
cured  patient  may  continue  to  harbor  and  scatter  these  dangerous 
microscopic  particles  of  living  matter  for  some  time,  thus  en- 
dangering other  members  of  the  community.  Possibly  self- 
infection  from  the  cysts  lodged  in  the  tissues  of  the  intestine  is 
the  cause  of  the  frequent  recurrence  of  infection  after  inadequate 
treatment,  but  it  is  more  probable  that  some  of  the  free  parasites 
escape  the  action  of  the  drug  and  continue  to  multiply  and  de- 
velop new  cysts.  Under  continued  treatment  the  cysts  gradually 
disappear  from  the  intestine,  but  their  exodus  is  hastened  by  purges. 

Bismuth  subnitrate  has  been  used  with  good  success  in  con- 
junction with  emetin,  the  bismuth  acting  as  a  sedative  on  the 
intestine  and  aiding  in  healing  of  the  lesions,  and  also  as  an  amebi- 
cide.  A  daily  enema  of  saline  solution  also  seems  to  aid  the 
efficiency  of  emetin. 

Another  preparation  of  emetin,  alcresta  ipecac,  is  effective 
against  dysentery  amebae,  though  not  so  certain  in  its  action 
as  the  hydrochloride.  It  has  an  advantage  in  that  it  can  be 
taken  in  the  form  of  tablets  when  a  physician  is  not  available 
and  the  apparatus  for  hypodermic  injection  is  not  at  hand. 
Some  doctors  in  southern  United  States  have  advocated  the 
use  of  extract  of  a  common  southern  plant,  Chaparro  amargosa, 
to  destroy  intestinal  amebae.  This  extract  is  very  cheap  and  en- 
tirely devoid  of  danger  in  ordinary  doses,  but  its  use  in  place 
of  emetin  has  not  yet  been  sufficiently  justified. 

Walker  and  Emrich  have  recently  (1917)  reported  the  success- 
ful use  of  oil  of  chenopodium  for  treatment  of  mild  cases  of  amebic 
dysentery,  and  especially  of  "carriers.''  It  is  pointed  out  that 
emetin  in  its  various  forms  is  often  inefficient  in  treatment  of 
carriers  on  account  of  its  powerlessness  against  encysted  amebae 


PREVENTION  OF  AMEBIC  DYSENTERY  130 

and  its  inability  to  eliminate  them.  These  investigators  em- 
phasize the  importance,  before  giving  the  oil,  of  a  preliminary- 
purgation  with  Epsom  salts  (magnesium  sulphate)  sufficient  to 
produce  fluid  bowel  movements,  the  purpose  being  both  to  re- 
move excess  faecal  matter  from  the  intestine  and  to  bring  the 
amebse  out  of  their  protective  cysts  and  subject  them  in  the 
unencysted  condition  to  the  action  of  the  chenopodium.  The 
treatment  found  most  effective  by  Walker  and  Emrich  is  as  fol- 
lows: (1)  magnesium  sulphate,  from  one-half  to  one  ounce, 
at  6  A.  M. ;  (2)  oil  of  chenopodium,  16  minims  in  gelatine  capsules 
(to  obviate  disagreeable  odor  and  taste),  at  8  a.m.,  10  a.m.  and 
12  M.,  and  (3)  castor  oil,  one  ounce,  containing  50  minims  chloro- 
form, at  2  p.  M.  This  or  any  other  treatment  should  be  followed 
by  examination  of  the  faeces  at  intervals  for  some  weeks  after 
treatment,  to  make  certain  of  the  cure. 

The  keynote  to  the  prevention  of  dysentery  whether  it  be 
caused  by  amebae  or  other  protozoans  or  bacteria  is  sanitation. 
The  efficacy  of  sanitary  measures  was  well  illustrated  by  the  fact 
that  during  the  first  month  of  the  occupancy  of  Vera  Cruz  by 
the  Americans  in  1914  there  were  four  times  as  many  cases  of 
dysentery  as  during  the  second  month  when  sanitary  measures 
had  been  taken  and  were  enforced.  The  fact  that  only  the  en- 
cysted parasites  as  found  in  the  fresh  or  dried  faeces  of  infected 
individuals  can  cause  disease  suggests  a  simple  remedy  in  the 
proper  disposal  of  infected  faeces.  In  tropical  countries,  however, 
such  a  preventive  measure  is  not  so  simple  as  it  sounds.  In 
many  districts  where  amebic  dysentery  is  endemic  the  first  ru- 
diments of  sanitation  are  unknown  and  every  possible  method  of 
transmission  of  amebic  dysentery  is  given  full  opportunity. 
Polluted  drinking  water,  uncleanHness,  transmission  by  flies, 
and  the  almost  universal  use  of  "  night-soil "  (human  faeces) 
for  fertilizer,  all  help  the  cause  of  dysentery  and  account  for  its 
prevalence. 

The  segregation  and  cure  of  dysentery  patients,  and  the  care- 
ful disposal  of  their  faeces,  is  not  enough  to  eradicate  the  disease 
entirely  since  there  are  many  immune  carriers  of  the  disease  who, 
though  apparently  well,  harbor  the  encysted  amebae  in  their 
faeces  and  thereby  constitute  a  source  of  danger  to  the  community. 
Thorough  sanitation  throughout  the  community  is  the  only  pre- 
ventive measure  which  is  adequate. 


140  AMEB^ 

Still  anotner  possible  factor  in  the  distribution  of  dysentery 
amebse  is  the  rat.  Dr.  Lynch  of  Charleston,  S.  C,  states  that  in 
that  city  rats  suffer  from  amebic  dysentery  as  well  as  man. 
The  fact  that  rats  became  infected  by  eating  infected  human 
fseces,  the  frequent  occurrence  of  the  disease  in  rats  in  houses 
where  human  amebic  dysentery  has  occurred,  and  the  ready 
transmission  of  the  disease  from  rat  to  rat  indicate  that  the  rat 
infection  is  identical  with  that  in  man,  and  is  not  due  to  the  ameba 
peculiar  to  rats,  E.  muris,  and  that  rats  may  play  an  important 
role  in  the  spread  of  the  human  infection.  It  may  be  that  rat 
destruction  will  prove  to  be  an  important  preventive  measure 
against  amebic  dysentery.  Chatton  has  recently  transmitted  the 
disease  to  guinea  pigs  also. 

Other  Intestinal  Amebae.  —  As  stated  above  there  are  a  number 
of  other  species  of  amebse  which  occur  as  human  parasites,  but  as 
compared  with  E.  histolytica  most  of  them  are  of  little  importance. 
They  are  not  tissue  parasites,  except  possibly  Councilmania 
lafleuri,  but  feed  principally  if  not  exclusively  on  bacteria  or  dead 
organic  matter  with  which  they  are  associated  in  the  intestine. 
Their  principal  importance  lies  in  the  possibility  of  their  confusion 
with  the  dysentery  amebse. 

One  of  the  commonest  species  is  Endamceha  coli.  In  stained 
preparations  this  species  can  be  distinguished  from  E.  histolytica, 
which  it  resembles  in  size  and  habitat,  by  the  characteristics 
given  on  p.  133,  (cf.  also  Figs.  36  and  37).  E.  coli  is  usually 
more  sluggish  in  movement  than  E.  histolytica.  It  never  con- 
tains blood  corpuscles,  but  the  body  is  often  filled  with  nu- 
merous food  vacuoles  containing  bacteria  or'  other  material 
ingested  from  the  intestinal  contents  (Fig.  37A).  The  cysts 
of  E.  coli  (Fig.  37B)  are,  on  the  average,  larger  than  those  of 
E.  histolytica,  but  as  with  the  latter  species  there  are  races  dis- 
tinguishable by  the  size  of  the  cysts.  The  average  sizes  in  differ- 
ent races  vary  from  15  /x  to  about  22  n.  The  mature  cysts  nor- 
mally contain  eight  nuclei  in  contrast  to  the  four  usually  found  in 
E.  histolytica.  Even  in  the  four-celled  stage  the  cyst  can  readily 
be  distinguished  from  those  of  E.  histolytica  by  the  eccentric 
position  of  the  karyosomes  of  the  nuclei.  According  to  Dobell 
"  E.  coli  has  been  found  living  as  a  harmless  commensal  in  the 
colon  of  man  wherever  and  whenever  it  has  been  sought :  no  race, 


INTESTINAL  AMEB^  141 

nor  any  country,  has  yet  been  discovered  in  which  infections  with 
this  species  are  not  common." 

There  is  no  effective  treatment  for  E.  coli  infections.  Since 
the  parasites  do  not  hve  in  the  tissues  they  are,  Uke  the  intestinal 
flagellates,  unaffected  by  emetin. 

Councilmania  lafleuri  (Fig.  41),  formerly  confused  with  En- 
damceba  coli,  has  recently  been  described  by  Kofoid  and  Swezy. 
The  free  amebae  are  very  active,  and  creep  about  with  re- 
markable rapidity.  They  commonly  produce  only  a  single  pseu- 
dopodium  at  a  time,  and  this  is  composed  entirely  of  clear 
ectoplasm.  The  pseudopodia  are  peculiar  in  that  they  are  shot 
out  almost  instantaneously  for  the  greater  part  of  their  length. 
The  endoplasm  is  usually  loaded  with  food  vacuoles  containing 
bacteria,  faecal  particles,  and  also  frequently  red  blood  corpuscles, 
the  latter  fact  indicating  that  this  parasite,  like  Endamceha 
histolytica,  is  in  part  a  tissue  parasite.  The  most  striking  and 
distinctive  characteristic  is  the  method  of  escape  of  amebulae 
from  the  cysts  by  a  repeated  process  of  budding,  a  single  nucleus 
at  a  time  slipping  out  through  a  pore  in  the  cyst  wall,  surrounded 
by  a  part  of  the  cytoplasm  (Fig.  41C).  It  is  probably  the  only 
parasitic  ameba  in  which  the  cysts  act  as  a  means  of  multiplica- 
tion without  transfer  to  a  new  host. 

Another  common  intestinal  ameba  of  man  is  Endolimax  nana, 
(Fig.  38),  the  principal  characteristics  of  which  are  given  under 
the  genus  Endolimax  on  p.  129.  It  is  a  small  ameba  measuring 
from  6  Ai  to  12  /z  (^uVir  to  -^^-^  of  an  inch)  in  diameter.  It  creeps 
sluggishly  like  E.  coli,  and,  like  that  species,  often  contains  numer- 
ous food  vacuoles  filled  with  bacteria.  The  four-nucleated  cysts 
(Fig.  38B)  might  be  confused  with  those  of  E.  histolytica,  but  are 
distinguishable  by  their  small  size  (usually  8  to  10  /z  by  7  to  8  /x), 
their  oval  shape,  and  the  peculiar  structure  of  the  nuclei,  described 
on  p.  129.  This  is  a  very  common  human  parasite,  having  been 
found  in  as  high  as  33  per  cent  of  some  series  of  examinations 
made  by  competent  workers.  Although  frequently  found  in 
dysenteric  patients  associated  with  Endamoeha  histolytica,  there 
is  no  evidence  that  this  species  is  at  all  pathogenic.  Like  E.  coli, 
this  ameba  cannot  be  eliminated  by  emetin  or  any  other  drugs 
although  it  temporarily  disappears  during  emetin  treatment. 
Its  exact  habitat  in  the  intestine  is  not  known,  but  it  is  certainly 
not  a  tissue  parasite. 


142  AMEB^ 

lodamoebe  butschlii  (Fig.  39)  is  a  small  ameba  (usually  9  m  to 
13  fx  in  length)  the  characteristics  of  which  have  been  sufficiently 
described  on  p.  132.  The  cysts  of  this  species  (Fig.  39B)  were 
until  recently  thought  to  be  of  vegetable  nature  and  were  known 
as  Iodine  or  I.  cysts.  The  cysts  are  not  smaller  than  the  free 
amebse;  they  are  of  very  irregular  shape,  as  if  formed  under 
pressure.  This  ameba,  also,  has  a  wide  geographic  distribution 
and,  while  not  so  common  as  the  intestinal  amebae  hitherto  dis- 
cussed, the  available  data  indicate  its  occurrence  in  from  3  per 
cent  to  5  per  cent  of  all  human  beings  in  temperate  or  tropical 
climates. 

Another  very  small  human  ameba,  Dientamoeha  fragilis  (Fig. 
40),  has  recently  been  described  by  Jepps  and  Dobell.  This 
species  averages  only  about  8  or  9  m  (^^^  of  an  inch)  in  diameter, 
thus  resembling  Endolimax  nana.  The  free  amebae  are  active, 
showing  well  marked  ectoplasm  and  endoplasm.  The  pseudo- 
podia  are  of  ectoplasm,  and  are  flat  and  leaf  like  (Fig.  40B).  The 
peculiar  features  of  the  organism  are  described  on  p.  129.  The 
most  characteristic  feature  of  this  ameba  is  the  division  of  the 
nucleus  shortly  after  cell  division  has  occurred,  so  that  mature 
individuals  have  two  similar  nuclei.  No  cysts  have  yet  been 
found,  yet  it  is  highly  improbable  that  the  infection  is  transmit- 
ted by  the  free  amebae,  since  the  latter  are  very  short-lived  outside 
the  body.  The  habits  of  the  organisms  are  probably  similar  to 
those  of  the  harmless  amebae  already  described.  Only  ten  cases 
of  infection  have  so  far  been  discovered,  but  the  evidence  afforded 
by  these  cases  indicates  a  wide  geographic  distribution. 

Mouth  Amebae 

The  occurrence  of  amebae  in  the  human  mouth  has  been  known 
for  many  years,  but  particular  interest  has  attached  to  them 
only  recently,  since  a  number  of  investigators  have  brought  forth 
evidence  to  show  that  the  common  mouth  ameba,  Endamoeba 
gingivalis,  is  pathogenic,  and  an  important  factor  in  pyorrhea. 

Pyorrhea,  or  Rigg's  Disease,  in  some  stage  afflicts  the  ma- 
jority of  all  adult  people,  and  over  50  per  cent  of  all  permanent 
teeth  which  are  lost  are  lost  as  the  result  of  pyorrhea.  The 
apparent  relation  between  this  disease  and  the  presence  in  the 
mouth  of  the  above-mentioned  ameba,  E.  gingivalis  (or  buccalis), 
was  first  demonstrated  in  1914  by  Smith  and  Barrett.     Since 


ENDAMCEBA  GINGIVALIS  AND  DISEASE  143 

then  there  has  been  much  controversy  as  to  the  role  played  by 
the  amebse  in  connection  with  the  disease,  and  most  authorities 
are  now  inclined  to  look  upon  the  amebae  as  having  little  or  no 
important  part  in  the  pathogenic  process,  but  this  question  cannot 
be  considered  as  settled.  The  prevalence  of  amebae  in  the  mouth, 
even  in  young  children,  is  well  shown  by  a  recent  investigation 
by  Anna  Williams  of  the  mouths  of  over  1600  school  children  in 
New  York  City.  Of  the  children  between  five  and  seven  years 
of  age  35  per  cent  were  found  infected,  while  of  those  between  five 
and  fifteen  years  60  per  cent  were  infected. 

The  mouth  ameba,  E.  gingivalis,  can  be  found  by  placing  a 
bit  of  the  pus  from  a  tooth  pocket,  or  the  scrapings  from  the 
teeth,  on  a  microscope  slide.  Here  the  parasites  will  be  found 
intermingled  with  pus  cells  and  bacteria.  They  are  from  one  to 
three  times  the  diameter  of  the  pus  cells,  usually  from  12  /*  to  20  m 
(ttjV^  to  T^Vir  of  an  inch)  in  diameter,  and  have  a  granular  ap- 
pearance; the  nucleus  is  relatively  very  small.  Often  when 
stained  they  show  dark  bodies  inside  of  them  which  are  probably 
the  nuclei  of  other  organisms  or  of  semi-digested  pus  cells.  When 
living  the  amebae  prowl  about  sluggishly,  pushing  out  a  blunt 
pseudopodium  now  on  one  side  of  the  body,  now  on  the  other,  then 
drawing  up  the  body,  and  pushing  out  more  pseudopodia,  thus 
slowly  working  their  way  about  between  the  pus  cells  and  frag- 
ments of  tissue.  The  outer  layer  of  the  body,  or  ectoplasm, 
which  serves  as  a  sort  of  protecting  envelope,  like  the  rind  on  a 
melon,  is  clear  and  transparent  but  is  not  readily  distinguishable 
except  when  the  animal  is  moving.  The  pseudopodia  are  always 
formed  first  out  of  this  clear  ectoplasm,  the  more  granular,  gray- 
ish inner  substance  or  endoplasm  pouring  out  into  it  later.  The 
reproduction  of  these  little  animals  is  by  a  simple  division  of  the 
body  into  two  when  they  have  grown  large  enough  to  feel  cumber- 
some as  single  individuals.  Although  cysts  have  been  described 
by  some  workers,  there  is  insufficient  evidence  for  their  existence, 
and  it  is  more  probable  that  infection  is  spread  by  simple  direct 
or  indirect  transfer  of  the  free  amebae  from  mouth  to  mouth. 

Some  investigators  have  suggested  the  possible  identity  of 
E.  gingivalis  and  E.  histolytica,  but,  as  pointed  out  by  Craig, 
the  sluggish  movements,  small  nucleus,  inability  to  produce 
dysentery  when  swallowed  and  other  characteristics  all  indicate 
that  without  doubt  the  mouth  ameba  is  quite  distinct  from  the 
intestinal  amebae. 


144 


AMEB^ 


-^-jaw 


Endamoeba  gingivalis  and  Disease.  —  As  intimated  above, 
although  the  presence  of  amebse  in  the  mouth  has  been  known 
for  many  years,  these  parasites  attracted  Httle  interest  until 
1914  when  several  investigators  called  attention  to  ah  apparent 
relationship  between  the  amebse  and  the  presence  of  pus  pockets 
between  the  teeth  and  gums,  a  disease  known  to  dentists  and 
physicians  as  "  pyorrhea  alveolaris."  The  amebse  do  not  thrive 
on  exposed  surfaces  in  the  mouth,  but  find  a  congenial  environ- 
ment in  any  little  secluded  pockets  between  the  teeth  and  gums, 
in  crevices  between  close-fitting  teeth,  or  where  a  bit  of  food  forms 
a  protected  spot  for  them.  Stowed  away 
in  such  places,  and  invariably  accompanied 
by  bacteria  and  often  spirochsetes,  they 
multiply  rapidly.  That  they  feed  largely 
on  other  organisms  cannot  be  doubted,  but 
that  they  prey  also  on  the  living  tissue 
cells  is  very  probable.  Eventually  the 
delicate  peridental  membrane  surrounding 
the  roots  of  the  teeth  (Fig.  42),  correspond- 
ing in  a  general  way  to  the  periosteum  of 
bones,  is  eaten  away  and  becomes  ulcerated. 
The  eating  away  of  the  living  membranes 
of  the  teeth  and  gums  is  accompanied  by 
a  constant  formation  of  pus,  and  a  marked 
proneness  for  the  gums  to  bleed,  often  with- 
out provocation.  The  swallowing  and  ab- 
sorption of  the  pus  and  of  the  poisonous 
waste  products  generated  by  the  parasitic 
organisms  are  probably  the  cause  of  the 
more  or  less  noticeable  constitutional  symptoms  which  accom- 
pany the  disease.  These  may  consist  of  feverishness,  dis- 
ordered digestion,  nervous  troubles,  rheumatic  pains  in  the 
joints,  anemia,  or  various  combinations  of  these  ailments.  We 
have  long  known  that  unhealthy  mouths  were  the  cause  of  gen- 
eral bad  health,  but  we  never  until  recently  had  any  definite  clue 
to  the  reason  why. 

As  the  ulceration  of  the  membrane  continues,  the  tooth  is 
gradually  loosened  from  the  gum.  Just  as  meadow  mice  girdle 
fruit  trees,  so  these  amebae,  or  the  bacteria  or  spirochsetes  which 
accompany  them,  eat  away  the  living  *'  bark  "  of  the  teeth  and 


perldcnt. 
p^riost. 


Fig.  42.  Sketch  of 
tooth  showing  peridental 
membrane,  which  is  the 
tissue  attacked  by  Enda- 
moeba gingivalis  and  the 
seat  of  pyorrhea,  peri- 
dent.,  peridental  mem- 
brane; periost.,  perios- 
teum; cr.,  crown;  r., 
root;  p.  pulp.  (After 
Bass  and  Johns.) 


AMEBiE  AND  PYORRHEA  145 

gums,  eventually  causing  the  teeth  to  fall  out.  As  already  stated, 
over  50  per  cent  of  all  permanent  teeth  which  are  lost  fall  out  as 
the  result  of  pyorrhea. 

Whether  the  formation  of  the  pus  pockets  is  initiated  by  the 
amebse  or  by  other  organisms  is  not  known,  but  certain  it  is  that 
Endamceha  gingivalis  is  with  few  exceptions  found  in  the  lesions, 
and  at  the  very  bottom  of  them,  often  burrowing  into  the  in- 
flamed tissues  to  a  depth  of  several  times  its  own  diameter,  de- 
vouring cells  and  transporting  bacteria.  The  belief  in  the  role 
of  the  amebse  is  based  on  these  facts  and  on  the  fact  that  often, 
though  not  always,  the  disease  is  greatly  improved  by  treatment 
with  emetin,  which  has  a  specific  action  on  amebic  dysentery. 
Some  investigators,  notably  Craig,  consider  it,  to  quote  from  Craig, 
"  more  than  doubtful  that  Endamceha  gingivalis  is  the  cause  of 
pyorrhea  alveolaris,  this  conclusion  being  based  upon  the  follow- 
ing facts:  the  occurrence  of  the  parasite  in  a  large  per  cent  of 
healthy  mouths  and  in  the  material  that  can  be  scraped  from 
healthy  teeth  and  gums;  the  occurrence  and  persistence  of  the 
parasite  in  patients  treated  with  emetin,  even  when  marked 
improvement  in  the  clinical  symptoms  have  occurred;  the  ab- 
sence of  the  parasite  in  some  typical  cases  of  pyorrhea;  the  lack 
of  improvement  with  emetin  shown  in  numerous  instances  of  the 
disease,  although  the  endamebae  may  disappear;  and  the  fact 
that  emetin  acts  upon  other  organisms  as  well  as  upon  endamebae 
and  the  possibility  that  the  improvement  that  often  follows  its 
administration  may  be  due  to  such  action  or  to  a  favorable  action 
on  the  tissue  cells."  That  these  facts  argue  against  the  causa- 
tion of  pyorrhea  by  amebae  alone  is  unquestionable.  These 
facts,  however,  are  not  only  not  opposed  to  the  possibiUty  of 
amebae  being  partly  or  indirectly  responsible  for  the  disease, 
but  may  be  interpreted  as  being  in  support  of  such  a  view.  It  is 
entirely  in  accord  with  the  known  facts  about  the  disease  to 
suppose  that  the  pus  pockets  may  be  initiated  or  enlarged  by  the 
action  of  amebae,  the  damage  being  then  continued  by  bacteria 
which  have  been  given  a  portal  of  entry.  This  would  account  for 
the  occasional  absence  of  amebae  in  typical  cases  of  pyorrhea  and 
for  the  occasional  cases  of  the  disease  which  are  not  improved  by 
emetin.  It  is  further  quite  conceivable  that  the  amebae  may  live 
for  a  long  time  in  crevices  in  the  mouth  without  doing  any 
damage,  and  yet  be  capable  of  causing  or  aggravating  pus  pockets 


146  AMEB^ 

under  suitable  conditions.  Perhaps  some  slight  injury  to  the 
membranes  or  the  combined  action  of  the  amebae  and  certain 
bacteria  is  necessary  to  start  the  process.  Parallel  cases  of 
parasites  which  may  hve  for  a  long  time  as  harmless  messmates 
and  then,  under  favorable  conditions,  become  pathogenic  are 
well  known;  one  of  the  best  examples  is  the  intestinal  ciliate, 
Balantidium  coli.  This  would  account  for  the  presence  of 
Endamceha  gingivalis  in  healthy  mouths.  It  is  significant  that  in 
her  investigation  of  school  children  in  New  York,  Anna  Williams 
found  only  30  per  cent  of  apparently  healthy  mouths,  and  94 
per  cent  of  mouths  with  spongy  and  bleeding  gums,  infected. 
As  to  the  statement  that  amebse  still  exist  in  pus  pockets  after 
treatment  with  emetin,  even  when  there  is  marked  improvement 
in  clinical  symptoms,  there  is  no  doubt  but  that  the  number  of 
amebse  is  greatly  reduced,  and  those  on  the  frontier  where  the 
most  damage  is  done  are  undoubtedly  killed,  since  they  are  most 
exposed  to  emetin  in  the  blood.  The  ineffectiveness  of  emetin 
against  amebse  which  are  not  directly  in  the  tissues  has  been 
demonstrated  in  the  case  of  the  intestinal  amebae  which  are  not 
tissue  parasites  (see  p.  139).  Again,  were  the  improvement 
following  treatment  with  emetine  due  to  favorable  action  on  the 
tissue  cells,  such  improvement  would  invariably  follow.  That 
emetin  affects  other  organisms  besides  amebae  is  true,  but  it  is 
more  active  against  these  protozoans  than  against  any  other  or- 
ganisms, as  far  as  is  known.  The  complete  cure  of  pyorrhea 
which  emetin  sometimes  effects,  the  usual  improvement  shown 
after  its  use,  and  the  occasional  failure  of  it,  all  point  to  the  in- 
strumentality of  amebae  in  causing  or  aggravating  the  disease, 
but  indicate  that  they  may  be  aided  and  abetted,  or  entirely  re- 
placed, by  bacteria  or  other  organisms. 

There  is  some  evidence  that  chronic  tonsilitis  also  is  often 
caused  by  E.  gingivalis,  since  this  parasite  is  found  in  the  ma- 
jority of  diseased  tonsils,  irritating  the  tissues  and  opening  the 
road  for  bacteria. 

An  indirect  relation  of  this  same  mouth  ameba  to  certain  types 
of  goitre  also  has  been  shown  to  be  very  probable.  Evans, 
Middleton  and  Smith  found  that  diseased  tonsils  and  nasal 
passages  and  enlarged  thyroid  glands  (goitre)  are  frequent  com- 
panions in  the  goitre  belt  of  Wisconsin.  They  believe  that  the 
amebse  injure  the  tissues  sufficiently  to  give  ample  opportunity 


PREVENTION  OF  AMEBiE  IN  THE  MOUTH         146a 

for  bacteria  to  enter  and  multiply  in  enormous  numbers,  and  that 
certain  of  these  bacteria  produce  poisonous  substances  which 
exert  a  stimulative  effect  on  the  thyroid  glands,  thus  causing 
goitre.  The  effect  of  the  presence  of  amebse,  indirect  as  it  is, 
can  be  fully  demonstrated  by  destroying  them  with  emetin.  In 
18  out  of  23  cases  of  goitre  treated  with  emetin  the  size  of  the 
thyroid  mass  was  obviously  reduced. 

Prevention  and  Treatment.  —  Ordinary  cleanliness  of  the 
mouth  by  frequent  brushing  of  the  teeth,  rinsing  of  the  mouth, 
and  care  of  imperfect  teeth  is  the  most  important  factor  in  keep- 
ing the  gums  healthy  and  free  from  an  injurious  degree  of  amebic 
infection.  In  the  investigation  of  school  children  in  New  York 
already  mentioned  the  number  of  ameba-infected  mouths  was 
reduced  one-half  by  ordinary  cleanliness  and  care.  Such 
methods,  however,  are  of  little  value  if  the  amebae  have  estab- 
lished themselves  in  a  pus  pocket,  since  in  such  situations  they 
cannot  be  reached  by  the  usual  methods  of  mouth  cleansing.  In 
the  New  York  investigation  it  was  found  that  mouths  could  almost 
always  be  freed  of  amebae  by  using  a  mouth  wash  with  a  weak 
solution  of  emetin,  the  latter  being  a  valuable  preventive  measure. 
In  older  people,  however,  where  the  amebae  have  often  already 
succeeded  in  stowing  themselves  away  in  little  crevices  and 
pockets  where  mouth  washes  cannot  reach  them,  some  other 
method  must  be  employed.  The  ideal  method  is  to  open  up  and 
thoroughly  clean  out  any  pus  pockets  which  can  be  found. 
This  should  be  followed  by  a  hypodermic  injection  of  emetin, 
repeated  on  a  few  successive  days  to  destroy  the  amebae  if  possible. 
The  effect  of  the  emetin  on  Endamoeba  gingivalis  is  not  as  marked 
as  was  formerly  thought,  and  Dobell  goes  so  far  as  to  say  "  it  thus 
seems  probable  that  emetin  has  no  specific  action  upon  E.  gingi- 
valis, and  that  the  original  claims  were  based  upon  insufficient 
evidence."  Usually  with  the  administration  of  emetin  the  sore- 
ness ceases,  the  pus  formation  stops,  the  gums  stop  bleeding  and 
the  general  health  rapidly  improves.  Of  course  it  takes  time  for 
the  injured  tissue  to  heal  and  the  part  destroyed  is  never  replaced. 
There  is  also  constant  danger  of  reinfection  and  the  already  eroded 
pocket  forms  an  excellent  place  for  fresh  amebae  to  take  up  a 
claim  and  begin  their  work.  Furthermore  there  are  cases  of 
pyorrhea  which  do  not  respond  to  treatment  with  emetin,  prob- 
ably because  the  work  is  continued  by  bacteria.     Emetin,  diluted 


146b  ameb^ 

200  to  400  times  in  alcohol  and  applied  with  a  tooth  brush, 
is  usually  sufficient  to  kill  recently  implanted  amebic  infections. 
A  thorough  mouth  rinse  with  a  drop  or  two  of  emetin  in  half  a 
glass  of  water  is  an  excellent  protective  measure  but  even  with 
the  use  of  these  means  of  prevention  some  apparently  cured  cases 
of  pyorrhea  get  reinfections  within  a  few  months. 

As  intimated  before,  the  prevention  of  infection  with  End- 
amoeba  gingivalis  is  largely  a  matter  of  ordinary  mouth  hygiene. 
Infection  can  be  avoided  to  a  large  extent  by  care  in  eating  and 
drinking.  One  should  never  eat  or  drink  with  the  same  articles 
that  have  been  used  by  other  people.  The  practice  of  promis- 
cuous kissing  is,  of  course,  a  ready  means  of  transmission  for 
these  parasites  as  for  many  others. 

Occasional  infection  with  Endamceha  gingivalis  is,  however, 
almost  inevitable.  If  the  mouth  is  kept  scrupulously  clean  and 
in  as  near  perfect  condition  as  possible  the  amebse  may  find  no 
congenial  place  to  settle  down,  but  in  the  vast  majority  of  mouths 
there  is  an  abundance  of  fertile  ground  for  them. 


CHAPTER  IX 
MALARIA 

Importance.  —  Of  all  human  diseases  there  is  none  which  is  of 
more  importance  in  the  world  today  than  malaria,  and  this  in 
spite  of  the  fact  that  we  have  a  very  full  knowledge  of  its  cause, 
the  manner  of  its  spread,  its  cure,  and  means  of  prevention.  It 
has  been  estimated  to  be  the  direct  or  indirect  cause  of  over  one- 
half  the  entire  mortality  of  the  human  race.  Sir  Ronald  Ross 
says  that  in  India  alone  it  is  officially  estimated  that  malaria  kills 
over  one  million  persons  a  year,  a  greater  number  of  deaths  than 
was  caused  by  the  great  European  war  in  the  first  two  years  of 
its  existence.  When  there  is  added  to  this  the  thousands  from 
the  rest  of  Asia,  Africa,  Southern  Europe,  South  and  Central 
America,  and  the  southern  part  of  our  own  country  who  are 
annually  sacrificed  on  the  altar  of  the  malarial  parasite;  the 
millions  of  others  who  are  broken  in  health,  incapacitated  for 
work  and  made  easy  victims  of  other  diseases;  the  valleys, 
countries,  and  even  continents  which  have  been  barred  from  full 
civilization  and  development  by  this  more  than  by  any  other 
cause;  then  only  can  we  get  a  glimpse  of  the  real  meaning  of 
malaria  to  man.  Ross  argues  convincingly  that  the  downfall 
of  the  great  Greek  empire  and  the  present  poverty-stricken 
bhghted  condition  of  many  parts  of  Greece  is  probably  due 
primarily  to  the  invasion  of  that  country,  not  by  burning  and 
devastating  armies  of  men,  but  by  the  malaria  parasite,  an  in- 
finitely more  terrible  though  unseen  foe  which  destroyed  the  new- 
born infants,  undermined  the  health  of  the  children  or  killed 
them  outright,  rendered  the  richest  agricultural  lands  uninhabi- 
table, and,  in  a  word,  sapped  the  vitafity  of  the  people  until  the 
boasted  power  and  glory  of  Greece  is  but  a  mocking  memory. 

Though  historians  and  economists  have  failed  to  recognize  it, 
the  r61e  of  malaria  and  other  endemic  diseases  must  have  played 
an  enormous  part  in  the  history  of  the  world  and  in  the  progress 
of  nations.     Malaria  and   its  powerful   accomplice,   the  hook- 

147 


148  MALARIA 

worm,  are  largely  responsible  for  the  present  deplorable  condition 
of  some  parts  of  our  own  South.  Dr.  Howard  estimated  in  1907 
that  there  were  nearly  12,000  deaths  a  year  in  the  United  States 
from  malaria.  This,  however,  is  probably  almost  inconsiderable 
when  the  amount  of  damaged  health  and  weakened  resistance  to 
other  diseases  is  taken  into  consideration.  Dr.  Von  Ezdorf ,  of  the 
U.  S.  Public  Health  Service,  in  a  recent  attempt  to  estimate  the 
prevalence  of  malaria  in  the  United  States,  obtained  data,  based 
on  morbidity  reports,  which  indicate  that  at  least  four  per  cent  of 
the  population  of  eight  southeastern  states  —  1,000,000  people 
—  is  affected  by  the  disease  annually,  and  found  by  13,526  blood 
examinations  that  over  13  per  cent  harbored  malarial  parasites 
in  their  blood,  the  percentage  being  much  higher  in  negroes 
than  in  whites.  Dr.  Howard  thinks  that  an  estimate  of  3,000,000 
cases  of  malaria  a  year  in  the  United  States  would  not  be  too 
high.  Millions  of  acres  of  fertile  land  in  this  country  are  rendered 
useless  or  only  imperfectly  cultivable.  Taking  everything  into 
consideration.  Dr.  Howard  makes  the  astounding  but  well- 
founded  statement  that  the  annual  financial  loss  to  the  United 
States  from  malarial  diseases  is  not  less  than  $100,000,000. 
This  is  the  condition  in  the  United  States,  a  large  portion  of  which 
is  relatively  free  from  malaria,  and  in  no  part  of  which  is  the  dis- 
ease so  prevalent  or  so  destructive  as  in  the  tropical  portions 
of  Asia,  Africa  and  South  and  Central  America.  In  a  broad  way 
one-third  of  the  population  of  highly  malarial  countries  suffer  from 
the  disease  annually.  According  to  Ross  the  number  of  deaths 
from  malaria  in  India  must  reach  1,300,000  every  year.  Obvi- 
ously the  importance  of  this  disease  to  mankind  is  not  Hkely  to 
be  overestimated. 

History.  —  "  Malaria  "  means  bad  air,  and  was  therefore  ap- 
plied to  a  number  of  fevers  which  were  commonly  associated 
with  the  bad  air  of  swampy  regions.  The  idea  that  malaria  is 
caused  by  bad  air,  unwholesome  odors,  damp  night  winds,  or 
impure  drinking  water  is  even  yet  adhered  to  not  only  by  some 
of  the  populace  but  even  by  a  few  unenlightened  medical  men. 
Ross  says  that  it  takes  ten  years  for  the  world  to  grasp  a  new 
idea,  but  his  estimate  is  far  too  low;  it  is  now  (1917)  37  years 
since  the  organism  causing  malaria  was  discovered  and  19  years 
since  its  transmission  by  mosquitoes  was  experimentally  proved. 
It  was  in  1880  that  Laveran,  a  French  army  surgeon  in  Algeria, 


MALARIAL  PARASITES  149 

discovered  a  parasitic  "  germ  "  which  he  proved  to  be  the  true 
cause  of  malarial  fevers.  Dr.  King,  of  Washington,  in  1883 
suggested  the  probabihty  of  malaria  parasites  being  spread  by- 
mosquitoes,  adducing  much  circumstantial  evidence  in  support 
of  his  views.  It  was  not  until  1898,  however,  that  Sir  Ronald 
Ross,  an  Englishman  in  the  Indian  Medical  Service,  experiment- 
ally proved  that  the  malaria  parasite  is  absolutely  dependent 
upon  certain  species  of  mosquitoes  for  its  transmission  from  man 
to  man.  Only  six  years  ago  (1911)  the  parasites  of  malaria  were 
first  successfully  cultured  outside  the  human  body  by  Bass  and 
Johns  at  New  Orleans,  a  feat  which  will  eventually  lead  to  new 
and  valuable  discoveries.  Other  workers  deserve  no  less  credit, 
perhaps,  for  suggestive  ideas,  or  for  additional  facts  concerning 
the  life  and  control  of  the  malarial  parasites.  The  ultimate 
results  of  their  discoveries  have  only  begun  to  be  felt,  but  al- 
ready such  enterprises  as  the  building  of  the  Panama  Canal  have 
been  rendered  possible.  The  Canal  could  never  have  been  built 
under  the  old  regime  of  medical  ignorance.  Statues  of  the 
pioneers  in  the  work  of  unraveling  the  truths  about  malaria 
and  yellow  fever  might  well  have  occupied  conspicuous  places 
at  the  Panama  Pacific  International  Exposition  at  San  Francisco. 

Malarial  Parasites.  —  Malarial  fevers,  of  which  there  are 
several  different  kinds,  we  now  know  to  be  caused  by  protozoan 
parasites  which  live  at  the  expense  of  the  red  blood  corpuscles, 
and  are  injected  into  the  human  body  and  transmitted  from 
person  to  person  only  by  the  bite  of  certain  species  of  mosquitoes. 

The  malarial  parasites  belong  to  the  protozoan  class  Sporozoa, 
or  spore  animals,  so  called  from  their  habit  of  reproducing  by 
breaking  up  into  a  number  of  small  parts  or  spores,  instead  of 
simply  dividing  into  two  as  do  most  of  the  Protozoa.  All  of  the 
Class  Sporozoa  are  parasitic  and  have  no  organs  of  locomotion 
when  full  grown.  Although  there  are  many  different  kinds 
which  live  as  parasites  in  other  animals,  very  few  normally  attack 
man  and  only  the  malarial  parasites,  belonging  to  the  genus 
Plasmodium,  are  of  primary  importance.  There  is  still  consider- 
able disagreement  as  regards  the  classification  of  the  human 
malarial  parasites.  Nearly  all  workers  on  the  subject  agree 
that  there  are  at  least  three  well-defined  species  of  Plasmodium 
causing  human  malaria,  and  there  is  some  evidence  that  distinct 
subspecies  or  varieties  of  some  of  these  occur.     The  commonest 


150  MALARIA 

and  most  widely  distributed  species  is  Plasmodium  vivax,  which 
causes  tertian  malaria.  Of  somewhat  more  limited  geographic 
range,  being  confined  to  tropical  and  subtropical  countries,  but 
of  infinitely  more  importance  on  account  of  the  deadly  nature  of 
its  attacks,  is  Plasmodium  falciparum,  the  cause  of  the  sestivo- 
autumnal  type  of  malaria,  also  called  malignant  tertian  or  subter- 
tian  fever.  During  the  hot  part  of  the  year  in  the  tropics  96  per 
cent  of  malarial  cases  are  of  the  sestivo-autumnal  type.  The  third 
species,  Plasmodium  malarice,  causing  quartan  malaria,  is  relatively 
uncommon,  though  more  frequent  in  temperate  than  in  tropical 
countries.  These  three  species  of  malarial  parasites  differ  from 
each  other  in  a  number  of  important  details  of  structure  and 
life  history  and  in  the  diseases  which  they  produce. 

Life  History  of  Plasmodium  falciparum,;  Human  Cycle.  — 
The  life  history  of  malarial  parasites  may  well  be  exemplified 
by  that  of  the  malignant  aestivo-autumnal  parasite,  Plasmodium 
falciparum,  as  diagrammatically  shown  on  Fig.  43.  When  first 
injected  into  the  human  blood  by  a  mosquito  the  animal  is 
exceedingly  minute  (Fig.  43 A).  It  immediately  enters  or  at- 
taches itself  to  a  red  blood  corpuscle,  where  it  grows  until  it 
occupies  one-half  or  two-thirds  of  the  corpuscle,  meanwhile  un- 
^dergoing  a  number  of  different  forms.  It  first  goes  through  a 
''signet  ring"  stage  (Fig.  43B),  the  ringlike  appearance  being 
due  to  the  presence  of  a  transparent  area  occupying  the  middle 
of  the  parasite,  while  the  tiny  round  nucleus  occupies  a  position 
at  one  side  of  the  parasite,  simulating  the  setting  in  a  ring.  As 
the  parasite  grows  larger  it  becomes  irregular  in  shape  (Fig.  43C) 
and  quite  active,  constantly  changing  its  form,  thrusting  out 
little  clublike  processes  or  pseudopodia,  now  here  and  now 
there.  Although  it  has  been  taken  for  granted  that  malarial 
parasites  penetrate  the  blood  corpuscles  and  live  inside  of  them 
recent  investigations  by  Mary  R.  Lawson  (Mrs.  Johnson)  indi- 
cate that  this  may  not  be  the  case  at  all,  but  that  the  parasites 
may  attach  themselves  to  the  surface  of  the  corpuscles,  squeezing 
up  little  mounds  of  the  substance  of  the  corpuscles  and  encircling 
these  mounds  with  their  bodies,  just  as  a  bit  of  skin  might  be 
squeezed  up  between  the  fingers.  Sometimes  several  parasites 
attach  themselves  on  top  of  each  other  around  a  single  mound. 
A  number  of  facts  give  support  to  Mrs.  Johnson's  theory:  it 
affords  a  logical  explanation  for  the  ring  forms  of  the  parasite;  it 


LIFE  HISTORY 


151 


3  ^  "  I 


r  60  p  fl 
•«»  -i^  5  S 

:      g    5    3 

-^  a  ...a 


4) 


o  fee's  Si 


N     to 


-n^-^.a 

a  •-  =^  i;; 

'3d  1^11 


^  3  ."^  ^ 

®       2,  o 

r1     fi     M  .^ 

.2  2  g.a 


■s 


Sh     tn     CO     o 

e3    O    a>    S 
;;3    M    tc    tc 


o  ^ '-'  a 


m5 

13    >> 

o  o 


.9  o 


M   w  °   c3 


r  "^  S  o     " 


E  -e;  a 


O  G  53 

(U   P-  a>  g 

>>  o  o 

-  a 


■s-l 


3  a 

13  .QJ 


1 


^    O    »-i      - 

^  a  e"^ 

^-^  H    (u    £3 

a 


Jt3    •  -  O  "^    3 
O    C     ,    ?3    iS 

§    S    2 

1 .2  a  §  -2 

CO         m         cr 


fl  +3' 


08   O 


c3 


•S!    <1> 


c3    o 


J  So  ^.2 

a  =«-s3 

b'C.2    . 

o  :    -;^  J3 


o  a  K  ^  ^ 

m    S   °^  "^  d 

i  a^'Sx 

i3  P  ..  a 


M' 


2 
»  o  a  M 

8  £-, 


ol  i-li 

j3    O    O    s     I 

oga^-1 


152  MALARIA 

explains  the  occasional  distinct  projection  of  the  parasites  at 

the  periphery  or  edge  of  the  corpuscles  (Fig.  44) ;  and  it  accounts 

for  the  ease  with  which  the  parasites  may  be  distorted  in  making 

blood   smears.     Another   argument  in  favor  of 

Othis  theory  as  opposed  to  the  intracorpuscular 
1         theory  is  that  the  haemoglobin  in  the  corpuscles 
'         is  believed  to  be  in  a  more  or  less  solid  state, 
A       and  would  therefore  make  it   difficult   for   the 
parasites,  if  situated  inside,  to  indulge  in  such 

O         active  movements  as  they  do.      The  majority 
of  protozoologists,  however,  have  not  accepted 
B      Mrs.  Johnson's  conclusions. 
As  the  parasite  develops  there   is  a  distinct 
Fig.  44.     Blood  tendency  for  the  affected  corpuscles  to  clump 

corpuscles  showing  '^  .  .      ^  ^ 

malaria    parasites  together,  thus  clogging  the  tiny  capillaries  which 
at   periphery.     B  ^^^  large  enough  to  allow  the  passage  of  only  a 

shows    two    para-      .      ^  T  r-  o  ^ 

sites    resting    one  smgle   corpuscle   at   a  time.     In   this  way   the 
??i°Tt-*^r   °*^^^'   capillaries  of  such  organs  as  brain,  spleen,  bone 

(Sketches  from  mi-         ^  °  ?     i-  ; 

crophotographs  by  marrow   and    others    may   be   obstructed   to    a 
Mary   Lawson  ^^^^^  degree.     Three-fourths  of  the  life  cycle  of 

[Mrs.  Johnsonj.)  °  .  .  ,  -^ 

the  parasites  is  usually  passed  in  the  plugged 
capillaries  so  that  only  during  one-fourth  of  their  cycle  can  they 
be  found  readily  in  the  circulating  blood. 

After  about  forty  hours  the  nucleus  of  the  parasite  divides  into 
a  variable  number  of  fragments,  usually  from  ten  or  15  to  as 
many  as  32,  i.e.,  under  favorable  conditions  it  may  split  five 
times,  into  two,  four,  eight,  16,  and  32  parts.  The  rest  of  the 
body  divides  itself  into  portions,  one  surrounding  each  fragment 
of  the  nucleus,  thus  forming  a  little  heap  of  ''  spores  "  (Fig.  43E) 
ready  to  burst  apart  and  leave  the  corpuscle  on  which  the 
parent  parasite  had  been  feeding.  In  the  center  of  the  heap 
can  be  found  a  little  mass  of  coal-black  pigment  granules,  the 
waste  products  resulting  from  the  digestion  of  the  oxygen- 
carrying  red  substance  of  the  blood,  haemoglobin.  When  the 
parent  parasite  bursts  the  young  parasites  formed  by  this  rapid 
process  of  multiplication  are  set  free  (Fig.  43F)  in  the  blood  where 
each  enters  a  new  corpuscle  and  repeats  the  process  of  growth 
and  reproduction.  The  pigment  and  other  waste  products 
which  are  left  behind  when  the  parasite  multiplies  are  released 
into  the  blood  stream  where  they  are  carried  to  all  parts  of  the 


NUMBERS  OF  PARASITES  153 

body  and  deposited  in  the  spleen  or  other  organs  or  under  the 
skin,  causing  the  sallow  color  so  characteristic  of  malarial  patients. 
It  is  at  the  time  of  the  bursting  of  the  corpuscles  and  release  of 
the  waste  matters  which  act  as  poisons  that  the  characteristic 
chills  and  fever  of  malaria  are  felt.  Since  the  cycle  from  one 
generation  to  the  next  is  usually  about  48  hours  in  the  sestivo- 
autumnal  parasite  the  attacks  of  ague  are  felt  at  these  intervals. 
In  this  malignant  type  of  malaria  the  bursting  of  all  the  para- 
sitized corpuscles  and  release  of  poisonous  waste  matter  does  not 
occur  so  nearly  simultaneously  as  it  does  in  the  other  species, 
the  result  being  that  the  paroxysms  of  chill  and  fever  are  drawn 
out  over  many  hours. 

A  "  quotidian  "  type  of  malignant  malarial  fever  in  which 
agues  occur  every  24  hours  is  occasionally  met  with,  the  parasites 
of  which  are  thought  by  some  authors  to  constitute  one,  or  even 
two,  distinct  species.  The  majority  of  cases  of  malaria  with 
daily-recurring  fevers  are  due  to  double  or  triple  infections,  the 
different  broods  maturing  on  different  days. 

This  rapid  process  of  multiplication  in  the  human  blood  re- 
sults in  a  short  time  in  an  enormous  number  of  parasites,  some- 
times many  billions.  The  actual  quantity  of  parasites  in  a 
human  body  in  a  case  of  severe  sestivo-autumnal  malaria  has 
been  estimated  at  600  cc,  or  over  one  pint.  It  may  or  may  not 
mean  more  to  the  reader  to  know  that  such  a  quantity  of  ma- 
larial parasites  would  number  3,000,000,000,000.  A  better  con- 
ception of  the  real  meaning  of  such  a  number  may  perhaps  be 
gained  when  it  is  realized  that  to  count  off  this  number  at  the 
rate  of  100  per  minute  day  and  night  without  cessation  would 
require  30  times  the  period  of  time  that  has  elapsed  since  the 
birth  of  Christ.  Eventually,  however,  either  the  parasite  kills 
its  host,  which  very  commonly  happens  with  this  particular 
species,  or  the  host,  by  the  development  of  a  temporary  immunity 
in  his  body,  kills  or,  as  it  more  often  happens,  suppresses  the 
parasite.  Such  a  course  of  events  unaltered,  would  lead  to  a 
very  early  and  complete  extermination  of  the  parasite.  There  is 
a  second  chapter  in  the  life  history  of  Plasmodium  which  saves 
it  from  such  an  early  death. 

After  the  parasites  have  been  developing  in  the  blood  for  about 
two  weeks  or  more  there  are  developed  special  sexual  forms  or 
gametocytes,  male  and  female,  in  the  form  of  sausage-shaped 


154  MALARIA 

crescents  (Fig.  43K  and  L).  Just  as  in  the  case  of  other  kinds 
of  animals  and  plants,  nature  has  adapted  these  animals  to  cope 
with  their  environment.  As  long  as  the  blood  of  their  host  forms 
a  suitable  environment  they  continue  to  multiply  in  the  normal 
manner,  but  when  conditions  due  to  the  formation  of  antibodies 
become  unfavorable  they  produce  these  sexual  crescents  in  large 
numbers  and  patiently  await  rescue  at  the  hands,  or  rather  the 
beak,  of  a  mosquito.  The  crescents  may  persist  in  the  blood  for 
several  weeks,  gradually  disappearing  after  all  other  symptoms 
of  infection  have  vanished.  Only  slight  differences  can  be  seen 
between  the  male  and  female  gametocytes,  the  female  being  more 
granular  in  appearance,  and  with  the  pigment  particles  arranged 
in  a  more  regular  triangular  manner  (Fig.  43K  and  L). 

Mosquito  Cycle.  —  When  sucked  into  the  digestive  tract  of  the 
mosquito  these  gametocytes  begin  a  complex  developmental 
cycle,  providing  conditions  of  temperature  are  favorable.  The 
most  favorable  temperatures  are  between  75°  and  85°  F.  The 
digestive  fluids  dissolve  the  remnant  of  the  blood  corpuscles,  but 
the  crescents  resist  digestion  (Fig.  43M  and  N)  and  become  more 
obviously  sexually  differentiated.  The  male  gametocyte  de- 
velops into  a  "  flagellated  body  "  (Fig.  43P),  a  little  sphere  from 
which  several  long  slender  filaments  project.  These  are  very 
active,  constantly  lashing  to  and  fro,  and  ultimately  break  loose 
and  wriggle  about  in  the  stomach  of  the  mosquito  like  little 
spermatozoa,  which,  in  effect,  they  are.  The  female  gameto- 
cyte develops  into  an  inactive  sphere  or  gamete  (Fig.  430)  and 
one  of  the  filaments  from  the  flagellated  male  enters  to  fertilize 
it  (Fig.  43Q).  How  perfectly  the  process  simulates  the  act  of 
fertilization  of  an  egg  by  a  spermatozoan  in  the  higher  animals! 

The  result  of  the  union  of  the  filament  from  the  flagellated 
body  with  the  inactive  female  gamete  is  a  body  which  corre- 
sponds in  every  way  to  a  fertilized  egg  of  a  higher  animal.  This 
new  individual,  the  beginning  of  a  new  generation,  grows,  elon- 
gates, and  becomes  quite  hke  a  little  worm  (Fig.  43  R).  It  now 
wriggles  and  worms  itself  about  in  the  stomach  of  the  mosquito 
and  penetrates  the  wall,  lodging  itself  between  the  inner  and 
outer  finings  of  the  stomach  (Fig.  43S).  Here  more  rapid  growth 
takes  place  and  a  heavy  capsule  develops,  protruding  on  the  outer 
surface  of  the  mosquito's  stomach  fike  a  wart  (Fig.  45).  Mean- 
while the  contents  of  the  capsule  undergo  important  changes, 


DEVELOPMENT  IN   MOSQUITO  155 

dividing  into  daughter  cells  (Fig.  43T)  from  each  of  which  slender 

spindle-shaped  bodies  project  like  the  "  stickers  "  on  a  chestnut 

burr  (Fig.  43 U).     Ultimately  the  cells  lose  their  identity  and 

the  entire  capsule  or  cyst  becomes  crammed 

full  to  the  bursting  point   with   myriads   of 

these  spindle-shaped  bodies  which  have  now 

developed  into  spores   (Fig.  43V).      Such  a 

capsule  may  contain  over  10,000  spores,  and 

there  may  be  as  many  as  500  capsules  on  a 

single  mosquito's  stomach  (Fig.  46).     About      fig.  45~*Cross  sec- 

12  days  or  more,  according  to  temperature,   tion   of   stomach    of 

after  the  infected  blood  was  swallowed  by  the  fr^Sr^^l^Zl'^i 

mosquito,  the  capsule  becomes   mature   and  subtertian      malaria. 

bursts,  releasing  the  spores  into  the  body  cavity  Qr^ssU*  ^^      ^    *^^ 

of  the  mosquito.    From  here  the  little  parasites 

make  their  way  to  the  three-lobed  salivary  gland  (Fig.  46,  sal.  gl.) 

lying  in  the  fore  part  of  the  thorax  and  connecting  with  the 

sucking  beak.     They  assemble  in  the  cells  lining  the  salivary 


Fig.  46.  View  of  digestive  tract  of  Anopheles,  showing  spore-filled  capsules  of 
malaria  parasites  on  wall  of  stomach,  pal.,  palpi;  prob.,  proboscis;  ant.,  antennae; 
ph.,  pharynx;  oes.,  oesophagus;  sal.  gl.,  salivary  glands;  f.  res.,  ventral  food 
reservoir;  d.  f.  res.,  dorsal  food  reservoirs;  prov.,  proventriculus ;  St.,  stomach; 
malp.  tub.,  malpighian  tubules;  int.,  intestine.      X  10. 

glands  (Fig.  43 W)  and  remain  there  perhaps  for  weeks,  until  the 
mosquito  bites.  When  this  happens  the  parasites  flow  with  the 
poisonous  saliva  into  the  puncture  made  by  the  mosquito  and, 
should  the  prey  of  the  mosquito  be  a  human  being,  the  whole 


156  MALARIA 

process  of  asexual  multiplication  in  the  human  blood  corpuscles 
begins  over  again.  Since  it  takes  ten  or  12  days  for  the  sexual 
cycle  to  be  completed  in  the  case  of  sestivo-autumnal  malaria, 
an  infected  mosquito  is  not  dangerous  for  at  least  this  length  of 
time  after  biting  a  malarial  patient.  However,  once  the  new 
generation  of  spores  has  been  developed,  the  mosquito  remains 
dangerous  for  several  weeks  and  may  infect  many  persons,  as  not 
all  the  parasites  are  poured  out  of  the  saUvary  glands  at  one 
biting. 

It  is  commonly  believed  that  malaria  parasites  not  only  do  not 
develop  but  cannot  live  in  the  mosquito  at  winter  temperatures, 
and  conflicting  results  have  been  obtained  from  experimentation. 
King  in  America  and  Wenyon  in  Macedonia  have  succeeded  in 
exposing  infected  mosquitoes  to  low  temperatures  without  destroy- 
ing the  parasites,  whereas  Mayne  (Mitzmain)  found  that  in 
Anopheles  infected  prior  to  hibernation,  healthy  normal  sporo- 
zoites  did  not  last  through  the  winter  in  the  salivary  glands.  Rou- 
baud  obtained  similar  results  in  France.  It  is  still  doubtful 
whether  the  malaria  parasites  normally  pass  the  winter  in  the 
mosquito  hosts  in  places  where  the  mean  temperature  falls  much 
below  60°  F.  for  any  considerable  time. 

Other  Species.  —  The  other  species  of  malarial  parasites  dif- 
fer only  in  minor  details  of  their  structure  and  development. 
The  tertian  parasite,  Plasmodium  vivax,  during  the  early  stages 
of  its  development  in  the  blood  corpuscles  is  extremely  active. 
Its  unceasing  restless  changing  of  shape  is  fascinating  to  watch 
under  the  microscope  and  one  feels  that  it  was  very  appro- 
priately named  "  vivax."  Unlike  the  malignant  parasites  of 
sestivo-autumnal  malaria,  the  tertian  parasites  do  not  tend  to 
clump  together,  and  so  do  not  become  plugged  in  the  capillaries 
but  remain  constantly  in  the  circulation.  To  this  fact,  as  will 
be  shown  later,  is  due  the  "  benign  "  nature  of  this  and  also  of 
the  quartan  parasite.  The  tertian  parasites  have  the  peculiarity 
of  growing  very  large  and  of  causing  the  corpuscles  which  they 
parasitize  to  enlarge  and  become  unhealthy  in  appearance. 
The  number  of  spores  which  result  from  the  sporulation  every 
48  hours  ranges  from  ten  to  25.  According  to  Ross  the  normal 
number  of  splits  of  the  nucleus  is  four,  which  would  result  in 
16  spores.  One  of  the  most  striking  points  of  difference  from 
the  "  malignant "  parasites  is  the  fact  that  the  gametocytes 


SPECIES  OF  PLASMODIUM 


157 


are  not  in  the  form  of  crescents,  but  instead  resemble  mature 
parasites  ready  to  sporulate.  A  comparison  of  Fig.  47 A,  A'  and 
A"  with  B,  B'  and  B"  and  C,  C  and  C"  brings  out  the  prin- 
cipal differences  among  the  three  species  of  parasites  as  regards 
size  at  maturity  (A,  B,  C),  number  of  spores  (A',  B',  C)  and  form 
of  gametocytes  (A",  B",  C"). 


Fig.  47.  Comparison  of  three  species  of  malaria  parasites  X  2000  (figures 
selected  largely  from  Manson).  A,  A'  and  A",  Plasmodium  vivax;  B,  B'  and  B'\ 
Plasmodium  malarioe;  C,  C  and  C",  Plasmodium  falciparum. 

A,  B  and  C,  mature  parasites  in  red  corpuscles. 

A\  B'  and  C,  segmented  parasites  ready  to  leave  corpuscles. 

A",  B"  and  C  ,  mature  gametocytes. 


The  quartan  parasite  more  closely  resembles  the  tertian  para- 
site in  flexibility  of  body  and  form  of  gametocytes  (Fig.  47B''),  but 
it  differs  in  that  it  does  not  cause  the  corpuscle  to  enlarge  (Fig. 
47B)  and  is  never  active  in  movements.  It  produces  only  from 
five  to  ten  spores,  the  nucleus  normally  undergoing  three  splits. 
The  spores  form  a  very  regular  rosette  or  '*  daisy-head,"  ar- 
ranging themselves  petal-like  around  the  dark  mass  of  pigment 
in  the  center  (Fig.  47B').  Unlike  either  of  the  other  parasites 
this  one  causes  ague  by  its  sporulation  once  in  72  hours  instead 
of  in  48  hours.  A  comparison  of  certain  phases  of  this  parasite 
with  the  same  phases  of  the  others  will  be  found  in  Fig.  47. 

Propagation.  —  As  remarked  above  infection  with  malaria  is 
now  known  to  take  place  exclusively  through  the  bites  of  certain 
species  of  mosquitoes,  all  belonging  to  the  genus  Anopheles  (in- 
cluding its  subgenera).     While  over  a  hundred  species  of  Anoph- 


158  MALARIA 

eles  have  been  described,  less  than  one-third  have  been  proved 
to  be  carriers  of  malaria.  Some  species  will  carry  certain  types 
of  malaria  and  not  others  (see  p.  439).  A  knowledge  of  the 
malaria-transmitting  ability  of  various  species  of  mosquitoes 
and  their  habits  is  of  the  utmost  importance  in  any  attempt  to 
exterminate  malaria  by  exterminating  mosquitoes.  The  knowl- 
edge that  A.  malefactor  of  Panama,  breeding  in  cavities  of  stumps 
and  trees,  was  not  a  malaria  carrier  saved  several  hundred  thou- 
sand dollars  in  the  anti-malarial  campaigns  in  the  Canal  Zone. 
The  distinguishing  characteristics  of  Anopheles  and  a  brief 
account  of  a  few  of  the  more  important  malaria-carrying  species 
will  be  found  on  pp.  439-441. 

Reports  of  malarial  outbreaks  have  occurred  which  were  said 
to  be  due  to  some  other  cause  than  mosquito  transmission,  but 
when  completely  investigated  there  has  always  been  found  to  be 
a  ''  leak  "  somewhere.  Sometimes  the  presence  of  mosquitoes 
was  unsuspected,  sometimes  other  fevers  have  been  mistaken 
for  malaria,  and  sometimes  the  malarial  parasites  have  been 
harbored  for  weeks  or  months  in  "  latent  "  form.  This  is  a 
phase  of  malaria  which  is  little  understood,  but  it  is  a  well-known 
fact  that  long  after  symptoms  of  the  disease  have  disappeared, 
and  the  parasites  can  no  longer  be  found  in  the  blood,  a  fresh 
outbreak  may  occur,  coincident  with  some  loss  of  vitality,  or 
some  physiological  shock  on  the  part  of  the  host  from  some 
other  cause.  Often  a  mere  change  of  climate  and  environment  is 
sufficient  to  precipitate  "  latent  "  malaria.  It  is  highly  probable 
that  the  ordinary  blood  parasites  are  carried  in  the  meantime 
in  such  small  numbers  as  to  be  practically  impossible  to  find. 
Ross  has  pointed  out  that  if  1000  parasites  in  the  body  were 
able  to  withstand  the  unfavorable  conditions  and  existed  there 
during  the  "  latent "  stages,  a  man  working  12  hours  a  day 
searching  blood  smears  would  have  a  chance  of  finding  one 
only  once  in  five  years.  Some  authors  have  advanced  the  theory 
that  the  gametocytes,  suddenly  stimulated  by  some  unknown 
cause,  develop  by  parthenogenesis,  i.e.,  without  the  ordinary  sexual 
mosquito  cycle,  and  thus  cause  the  relapse.  This  idea  has  been 
widely  accepted  but  there  seems  to  be  little  ground  for  it  and  some 
positive  evidence  against  it.  The  parasites  naturally  thrive 
best  when  their  host  is  weakened  by  some  other  influence  which 
then  acts  as  an  accomplice  for  them.     Such  influences  are  ex- 


COURSE  OF  DISEASE  159 

posure  to  sudden  changes  in  climate,  fatigue,  dissipation  and 
other  sickness.  Even  educated  people  often  come  to  believe 
that  malaria  is  directly  caused  by  these  conditions. 

Suffice  it  to  say  that  many  experiments,  carried  out  with  the 
utmost  care  and  accuracy,  and  checked  by  numerous  repetitions, 
have  proved  beyond  doubt  that  the  mosquito  is  the  necessary 
transmitter  and  intermediate  host  of  malarial  parasites.  A  few 
investigators  think  it  possible  that  other  animals  besides  man 
may  serve  as  hosts  for  the  malarial  parasites,  so  that  malaria 
may  occur  even  in  uninhabited  regions.  Although  many  para- 
sites are  able  to  live  in  a  number  of  different  kinds  of  animals, 
this  does  not  seem  to  be  true  with  the  malarial  parasites,  and 
all  attempts  to  infect  even  monkeys  have  so  far  failed.  Until 
some  definite  proof  of  the  role  of  some  other  animal  as  a  host 
for  human  malarial  parasites  has  been  brought  forward  we  may 
look  upon  this  as  very  improbable.  Possibly  the  alleged  presence 
of  malaria  in  uninhabited  regions  may  be  explained  by  the 
malarial  parasites  in  the  mosquito  passing  into  the  eggs  of  the 
mosquito,  and  thus  being  carried  on  generation  after  generation. 
Though  the  germs  of  some  diseases  are  known  to  do  this  in  their 
insect  hosts,  experiments  with  hereditary  transmission  of  ma- 
larial parasites  in  mosquitoes  have  so  far  been  unsuccessful. 

The  Disease.  —  Malaria  as  a  disease  is  extremely  variable. 
A  "  typical  "  case  of  malaria,  in  the  tropics  at  least,  is  a  rather 
unusual  thing.  As  we  have  seen,  there  are  at  least  three  different 
kinds  of  malarial  parasites,  each  of  which  produces  a  somewhat 
different  disease.  While  ordinarily  all  the  parasites  of  a  brood 
mature  at  regular  intervals,  a  person  in  a  malarial  district  may 
be  infected  with  two  or  more  broods  maturing  at  different  times, 
and  the  case  may  be  farther  complicated  by  a  "  mixed  ''  infec- 
tion, that  is,  by  more  than  one  species  of  malaria  at  a  time. 
Varying  degrees  of  immunity,  the  effects  of  insufficient  quinine 
or  other  drugs,  the  presence  of  complicating  diseases  and  the 
virulence  of  the  particular  strain  of  parasites  all  have  a  hand  in 
modeling  the  effects  produced  by  "  malaria."  It  is  little  wonder 
that  in  some  places  practically  every  ailment  or  feeling  of  "  ma- 
laise "  is  attributed  to  malaria.  In  the  tropics  such  a  diagnosis 
would  be  correct  in  a  great  many  cases.  However,  the  habit 
of  attributing  any  indisposition  which  cannot  be  accounted  for 
otherwise  to  malaria  has  been  transplanted  into  non-malarial 


160  MALARIA 

places,  and  it  is  not  uncommon  to  hear  of  a  person  having  a 
''  touch  of  malaria  "  when  in  reahty  he  has  only  indigestion,  a 
cold  or  a  light  case  of  la  Grippe.  It  is  largely  due  to  this  fact 
that  malaria  is  looked  upon  in  non-malarial  districts  as  of  such 
small  consequence. 

The  early  stages  of  all  types  of  malaria  are  similar  except  that 
the  quartan  type  produces  the  intermittent  fevers  on  every  third, 
instead  of  every  second,  day.  During  the  incubation  period  of 
the  disease  there  is  a  feeling  of  ennui  with  headache  and  perhaps 
slight  fever.  After  about  a  week,  when  the  parasites  have  mul- 
tiplied to  150,000,000  or  more,  the  regular  intermittent  fevers 
set  in.  Each  attack  begins  with  a  shivering  chill,  sometimes 
accompanied  by  convulsions,  so  severe  that  the  teeth  chatter 
and  goose-flesh  stands  out  all  over  the  body.  Yet  the  tempera- 
ture will  be  found  to  be  several  degrees  above  normal,  and  still 
going  up.  In  the  wake  of  the  chill  comes  a  burning  and  weak- 
ening fever,  with  violent  headache  and  vomiting  and  a  tempera- 
ture from  six  to  eight  degrees  above  normal.  The  fever  stage  in 
turn  is  followed  by  a  period  of  sweating,  so  profuse  that  the 
clothes  or  bedding  may  become  wringing  wet.  The  sweating 
gradually  subsides,  the  temperature  drops  rapidly,  often  below 
normal,  and  the  patient,  after  from  six  to  ten  hours  in  the  case 
of  benign  infections  and  about  20  hours  in  malignant  infections, 
rests  fairly  easy  until  the  next  attack.  The  fact  that  the  attacks 
most  commonly  occur  between  midnight  and  noon,  instead  of  in 
the  evening,  is  often  useful  in  distinguishing  malaria  from  other 
intermittent  fevers. 

In  the  case  of  ''  benign "  (tertian  and  quartan)  infections 
after  these  agues  have  recurred  for  about  ten  days  or  two  weeks, 
the  symptoms  gradually  subside  and  the  patient  experiences  a 
rally.  From  this  point  either  he  may  recover  completely  (even  if 
untreated)  or  he  may  suffer  a  relapse  with  all  the  old  symptoms  of 
regular  agues.  Then  comes  another  rally  and  a  second  relapse, 
this  continuing  for  months  or  years,  aided,  perhaps,  by  constant 
reinfections.  During  all  this  time  general  symptoms  of  emaci- 
ation, sallowness,  anemia  and  enlarged  spleen  constantly  in- 
crease at  a  diminishing  rate  with  each  elapse,  and  decrease  at 
a  similarly  diminishing  rate  with  each  rally,  so  that  eventually  a 
fairly  constant  state  of  spleen-enlargement,  emaciation,  anemia, 
sallowness  and  general  run-down  condition  is  arrived  at  —  the 


BLACKWATER  FEVER  161 

well-known  condition  of  chronic  malaria,  or  malarial  cachexia, 
common  especially  in  children.  The  spleen  enlargement  is  the 
most  readily  recognizable  symptom  of  chronic  malaria  and  there- 
fore the  '*  spleen  rate,"  i.e.,  the  percentage  of  enlarged  spleens 
in  a  community,  gives  a  fairly  accurate  measure  of  the  prevalence 
of  malaria  to  which  some  degree  of  immunity  has  been  developed. 
Usually,  unless  the  weakened  condition  has  given  some  other 
disease  a  chance  to  put  an  end  to  it  all,  a  general  improvement 
ultimately  begins.  This  is  especially  true  in  children,  so  that 
by  the  time  they  reach  adult  life  they  are  in  fairly  good  health 
and  immune  to  malaria. 

In  the  case  of  sestivo-autumnal  or  malignant  malaria  the 
course  of  the  disease  is  often  not  so  light,  and  early  death  is  not 
a  rare  occurrence.  The  fact  that  the  bodies  of  the  malignant 
parasites  clump  together  and  plug  the  capillaries,  thus  preventing 
the  proper  flow  of  blood  in  the  vital  organs,  is  probably  the  chief 
cause  of  their  malignant  nature.  One  of  the  most  certain  symp- 
toms of  a  malignant  attack  of  malaria  is  a  total  loss  of  conscious- 
ness or  coma,  due  to  a  plugging  of  the  capillaries  in  the  brain. 
Indeed,  50  per  cent  of  the  deaths  from  malaria  are  said  to  be 
caused  by  a  plugging  of  the  brain  capillaries.  The  type  of  brain 
disease  which  may  be  caused  is  very  variable  but  some  mental 
disturbance  almost  always  occurs,  and  may  take  place  at  almost 
any  time  during  the  course  of  the  disease,  though  it  never  occurs 
during  the  first  fever  fit,  probably  because  the  parasites  are  not 
yet  numerous  enough  to  do  any  great  damage. 

In  connection  with  malarial  fevers  there  must  be  mentioned 
a  much  dreaded  and  little  understood  condition  known  as  '^  black- 
water  fever."  This  is  a  disease  in  which  something  destroys 
the  red  blood  corpuscles  in  large  numbers,  causing  the  coloring 
matter  of  the  blood,  haemoglobin,  to  be  liberated,  eventually  to 
be  voided  with  the  urine,  giving  the  latter  a  very  dark  color. 
At  the  same  time  there  is  a  more  or  less  irregular  fever,  biHous 
vomiting  and  severe  aches.  In  a  gi'eat  many  cases  it  results  in 
death.  This  disease  has  usually  been  considered  as  an  outcome 
of  severe  malaria,  since  it  always  occurs  in  malarial  countries 
and  usually  follows  or  accompanies  an  attack  of  malaria.  It 
is  not  uncommon  in  southeastern  United  States,  some  parts  of 
tropical  Africa,  southern  Europe  and  many  parts  of  tropical 
Asia  and  the  East  Indies.     In  many  other  malarial  districts  it 


162  MALARIA 

is  entirely  absent.  It  is  suggested  by  Manson  that  the  fever  is 
caused  by  a  distinct  organism,  and  that  malaria  is  merely  a 
predisposing  cause. 

Immunity  and  Epidemics.  —  Absolute  immunity  to  malaria 
is  rarely  if  ever  acquired  but,  as  already  remarked,  oft-repeated 
infections  especially  in  childhood  tend  to  build  up  a  high  de- 
gree of  tolerance  to  the  effects  of  the  parasites  and  a  diminution 
in  the  number  of  parasites  in  the  body.  The  protection  afforded 
by  a  single  infection  is  very  slight,  and  is  retained  for  only  a 
short  time  in  the  absence  of  reinfections.  Even  the  cumula- 
tive effect  of  numerous  infections  disappears  rapidly  in  the 
course  of  a  few  years.  Some  authors  divide  malaria  into  two 
types.  There  is  a  *'  tropical  "  form,  occurring  in  places  where 
reinfections  can  occur  practically  throughout  the  year  on 
account  of  the  continued  warm  temperature.  The  other,  a 
"  subtropical  "  form,  is  found  in  regions  where  cold  weather 
causes  an  annual  seasonal  interruption  of  infection  by  a  cessation 
of  breeding  on  the  part  of  Anopheles,  and  by  a  discontinuance  of 
growth  on  the  part  of  the  parasites  in  the  mosquitoes.  In  tropi- 
cal malaria  a  fairly  constant  degree  of  immunity  is  maintained, 
and  epidemics  are  rare  if  they  occur  at  all.  In  Java  and  other 
tropical  places,  according  to  Robert  Koch,  nearly  every  native 
child,  under  four  years  of  age,  has  his  blood  teeming  with  ma- 
laria parasites  from  which  he  suffers  little  inconvenience.  These 
parasites  gradually  become  scarcer  in  older  children  and  are 
often  practically  absent  in  adults  who,  however,  have  been  shown 
to  be  passive  "  carriers  "  of  small  numbers  of  the  parasites  and 
therefore  a  source  of  danger  to  the  community.  The  "  carriers,'* 
though  relatively  immune  to  the  more  acute  symptoms  of  the 
disease,  are  left  in  the  run-down  condition  of  malarial  cachexia. 
As  pointed  out  by  Gill,  there  is  a  striking  analogy  between  the 
confirmed  opium-eater  and  the  malarial  cachectic.  Both  have 
purchased  their  immunity  at  a  heavy  price.  In  the  former  the 
emaciated  frame,  sallow  complexion  and  other  signs  of  debility 
proclaim  the  victim  of  a  drug  habit;  in  the  latter  the  enlarged 
spleen,  the  lack  of  physical  and  mental  energy,  and  the  shrunken 
body  bear  witness  to  the  havoc  wrought  by  long-standing  ma- 
laria. In  the  case  of  neither  does  death  often  take  place  as  the 
direct  effect  of  their  respective  poisons,  but  both  readily  fall 
victims  to  intercurrent  affections.     In  subtropical  malaria,  on 


TREATMENT  163 

the  other  hand,  the  average  tolerance  of  the  community  to  the 
disease  suffers  an  annual  relapse,  and  may  constantly  decrease 
for  a  number  of  years.  When  the  immunity  of  the  community 
as  a  whole  becomes  quite  low,  and  there  is  a  sudden  increase  in 
the  probability  of  infection  by  a  great  increase  in  number  of 
mosquitoes,  accompanied  possibly  by  an  influx  of  infected  people, 
an  epidemic  of  the  disease  may  occur  of  such  extraordinary  se- 
verity as  to  involve  almost  the  entire  population,  and  to  cause  a 
mortality  of  several  hundreds  per  thousand.  Such  devastating 
epidemics,  probably  of  the  subtertian  type  of  malaria,  have  been 
termed  ''fulminant  malaria"  and  are  believed  to  occur  quite 
extensively  in  malarial  countries  lying  just  outside  the  region  of 
"  tropical "  malaria.  Fulminant  malaria  in  especially  severe 
form  occurs  periodically  in  parts  of  India  and  in  Italy. 

It  was  formerly  thought  that  considerable  racial  immunity 
protected  the  negro  races,  but  it  has  been  shown  that  in  many 
cases,  at  least,  the  immunity  has  been  acquired  by  constant 
exposure  to  the  disease,  and  that  it  disappears  upon  removal  from 
infected  regions.  The  whites  in  southern  United  States  are  said 
to  suffer  markedly  more  from  malaria  than  do  the  negroes  though 
the  latter  are  more  frequently  parasitized,  but  this  may  be  due, 
in  part  at  least,  to  the  more  permanent  residence  of  the  latter 
in  the  malarial  districts.  As  said  before,  individual  resistance 
to  the  effects  of  the  disease  is  variable.  Occasionally  there  is 
found  a  fortunate  individual  who  is  naturally  absolutely  immune, 
but  this  is  a  very  rare  occurrence. 

Treatment.  —  It  is  one  of  the  greatest  blessings  in  the  world 
that  we  have  for  malaria  a  definite  and  specific  cure  as  near  to 
being  a  "  sure  cure  "  as  has  been  discovered  for  any  disease. 
Quinine  has  been  found  absolutely  destructive  to  malarial  para- 
sites. While  a  dose  of  quinine  given  during  a  fever  attack  will 
not  act  quickly  enought  to  cut  it  short,  it  will,  if  given  immediately 
after  an  attack,  prevent  the  next  one,  or  at  least  alleviate  it. 
Meanwhile  the  organisms  disappear  from  the  circulation.  It  is 
usually  supposed  that  they  are  directly  killed  by  the  quinine, 
which  acts  as  a  virulent  poison  for  them,  though  this  is  doubted 
by  some  workers.  The  methods  of  administering  quinine  must, 
of  course,  vary  with  the  age  and  condition  of  the  patient,  and  the 
state  of  the  disease.  Sometimes  very  speedy  action  is  needed, 
and  it  is  not  safe  to  wait  for  quinine  to  be  slowly  absorbed  from 


164  MALARIA 

the  stomach.  Many  a  patient  has  died  from  malaria  with 
enough  quinine  in  his  stomach  to  have  saved  his  hfe  had  it  been 
properly  given.  In  such  cases  injections  into  the  muscles,  or 
still  better,  directly  into  the  veins,  is  necessary.  In  malignant 
malaria  quinine  does  not  reach  the  parasites  plugged  in  the 
capillaries  and  therefore  can  destroy  them  only  as  they  sporulate 
and  get  back  into  the  circulation.  Since  the  parasites  of  this 
type  often  sporulate  at  irregular  intervals  a  constant  supply  of 
quinine  at  a  killing  concentration  must  be  kept  in  the  blood. 
However,  overdosing  with  quinine  is  not  an  uncommon  fault 
with  physicians.  Quinine  poisoning  in  some  respects  resembles 
malarial  symptoms  and  the  physician,  thinking  the  latter  are 
not  abating,  gives  still  more  quinine  until  the  patient  succumbs 
to  it.  Not  a  few  malarial  deaths  are  really  due  to  excessive 
quinine.  Malarial  specialists,  such  as  Professor  Bass  of  New 
Orleans,  say  that  it  is  never  necessary  to  give  more  than  ten  or 
possibly  fifteen  grains  of  quinine  at  a  time,  if  given  as  the  case 
requires  it.  Twenty  grains  of  quinine  sulphate  a  day  taken  by 
mouth  in  several  doses  for  a  period  of  two  weeks  is  said  by  Bass  to 
disinfect  anyone.  Quinine  must  be  avoided  during  or  immedi- 
ately following  an  attack  of  blackwater  fever,  since  the  symptoms 
of  this  malady  are  intensified  by  its  use. 

In  case  of  severe  malarial  cachexia,  the  only  safe  course  is  for 
the  patient  to  leave  the  malaria-infected  country  in  which  he 
has  been  living,  and  stay  away  for  an  extended  period  of  time. 
He  should  take  regularly  small  doses  of  quinine  to  kill  any  lurk- 
ing parasites  which  may  remain  in  his  body,  and  do  everything 
possible  to  build  up  his  general  health  and  to  regain  his  lost 
vitality. 

Prevention.  —  The  prevention  of  malaria  is  a  problem  that 
should  be  solved  not  by  individuals  but  by  civic  effort.  Ross 
says:  ''  It  (malaria)  is  essentially  a  political  disease  —  one  which 
affects  the  welfare  of  whole  countries;  and  the  prevention  of  it 
should  therefore  be  an  important  branch  of  public  administration. 
For  the  state  as  for  the  individual  health  is  the  first  postulate 
of  prosperity.  And  prosperity  should  be  the  first  object  of 
scientific  government." 

Since  the  malarial  parasites  have  two  hosts,  man  and  mosquito, 
the  possibility  of  exterminating  them  in  either  host  presents  itself. 
Stephensport,  in  New  Guinea,  was  practically  cleared  of  malaria 


PREVENTION  165 

in  a  few  months  by  destroying  the  parasites  in  man  by  whole- 
sale "  quininization."  In  most  places,  however,  the  difficulties 
connected  with  this  method  of  extermination  are  even  greater 
than  those  associated  with  its  alternative,  the  destruction  of 
malarial  mosquitoes.  The  relation  of  partially  or  entirely  im- 
mune ^'  carriers  "  to  the  spread  of  malaria  is  of  extreme  impor- 
tance and  is  usually  greatly  underestimated.  The  number  of 
such  apparently  healthy  carriers  in  malarial  districts  is  astonish- 
ingly large.  Eradication  of  malaria  by  attacking  it  in  man  would 
entail  the  persistent  and  thorough  quinine  treatment  of  all  these 
carriers  as  well  as  of  patients. 

Undoubtedly  in  practically  every  case,  if  accompanied  by  as 
extensive  a  use  of  quinine  as  is  possible,  eradication  of  malarial 
mosquitoes  is  the  most  effective  and  most  permanent  preventive 
measure.  A  discussion  of  methods  of  reducing  and  controlling 
such  mosquitoes  will  be  found  on  pages  455^62. 

Complete  extermination  of  malarial  mosquitoes  is  not  necessary 
to  reduce  or  even  to  eradicate  malaria  entirely.  Ross  has  shown 
by  mathematical  computation  that  a  relatively  high  number  of 
malarial  mosquitoes  per  person  is  necessary  in  a  community  to 
propagate  malaria  successfully.  A  small  deviation  above  or 
below  a  certain  number  of  malarial  mosquitoes,  probably  between 
40  and  60  per  person  during  a  month,  a  deviation  too  small  to 
be  detected  readily,  will  mean  the  difference  between  an  ulti- 
mate extermination  of  the  disease  and  its  permanent  estabUsh- 
ment.  Ross  also  shows  that  the  relation  between  the  amount 
of  malaria  in  a  given  region  and  the  number  of  malarial  mosqui- 
toes is  so  definite  that  it  can  be  mathematically  computed. 
These  facts  are  of  importance  in  the  fight  against  malaria  since 
they  demonstrate  to  us  that  we  do  not  have  to  exterminate 
totally  even  the  malaria-carrying  species  of  Anopheles  in  order 
to  exterminate  malaria,  and  our  task  becomes  much  less  difficult. 
By  this  partial  extermination  some  of  the  most  malarial  districts 
in  the  world  have  been  practically  freed.  Up  to  1900  over  16,000 
deaths  a  year  from  malaria  occurred  in  Italy;  now  they  may  be 
counted  in  hundreds.  One  of  the  first  demonstrations  of  what 
could  be  accomplished  by  mosquito  extermination  was  made  by 
Major  Ross  in  1902  at  Ismailia  on  the  Suez  Canal  where  from 
1100  to  2500  cases  of  malaria  occurred  annually  in  a  population 
of  less  than  10,000.     Four  years  later  not  a  single  new  case 


166  MALARIA 

occurred  there.  The  same  thing  on  a  much  larger  scale  was 
accomplished  in  the  Canal  Zone  at  Panama  by  Surgeon-General 
Gorgas  and  his  staff.  On  this  relatively  large  malaria-infested 
area  the  death  rate  for  the  total  population  of  about  100,000  was 
reduced  64  per  cent  in  four  years.  The  deaths  from  malaria 
were  reduced  about  85  per  cent  in  less  than  four  years,  and  yellow 
fever  was  totally  eradicated.  Similar  feats  have  been  accom- 
plished at  Havana,  Staten  Island,  and  other  places.  One  of  the 
most  recent  examples  of  what  can  be  done  was  furnished  by  the 
American  occupation  of  Vera  Cruz  in  1914.  The  American  troops 
were  severely  attacked  by  malaria  of  all  three  types,  and  an  anti- 
mosquito  campaign  was  immediately  inaugurated.  It  cost  the 
Sanitary  Department  $5000  a  month  to  oil  the  pools,  drain  the 
low  parts  of  the  city  and  its  environs,  and  dispose  of  the  standing 
water  in  street  gutters,  refuse  heaps,  etc.,  but  in  a  few  months 
Vera  Cruz,  one  of  the  most  deadly  malarial  districts  in  the  world, 
was  practically  freed  from  Anopheles,  and  danger  of  malaria 
reduced  to  almost  nothing. 

Obviously  the  wholesale  reduction  or  extermination  of  malarial 
mosquitoes  can  be  accomplished  only  by  communities  or  by 
government  aid.  San  Antonio  has  freed  itself  of  mosquitoes 
and  mosquito-borne  diseases  by  enlisting  the  services  of  the 
school  children.  In  our  southern  states,  where  there  are 
65,000,000  acres  of  swamp  land,  and  where  the  chief  malarial 
mosquitoes  are  swamp  breeders,  malaria  can  never  be  destroyed 
until  state  and  federal  governments  are  willing  to  invest  money 
as  readily  to  take  water  off  the  land  in  these  parts  of  the  country 
as  they  now  invest  it  to  put  water  on  the  land  in  the  arid  western 
parts. 

Much  can  be  done  toward  reduction  of  malaria  in  selecting 
dry  brushless  sites  for  houses  and  in  constructing  them  in  mos- 
quito-proof fashion.  The  houses  one  sees  in  the  American 
Government  settlements  on  the  Canal  Zone,  built  well  up  off 
the  ground  and  with  open  sleeping  porches,  wide  verandas  and 
airy  windows,  all  carefully  screened,  are  ideal  for  tropical  dis- 
tricts where  malaria  and  other  insect-borne  diseases  are  common. 
They  present  a  happy  combination  of  airiness,  sanitation,  and 
complete  protection  from  insect  pests. 

In  well-known  malarial  districts  it  is  a  good  personal  safeguard 
to  use  screens  as  much  as  possible  and  to  take  regular  doses  of 


QUININIZATION  167 

quinine  at  all  times  as  a  preventive  measure.  In  the  pine  swamps 
and  along  the  coasts  of  Florida  malaria  is  practically  absent  on 
account  of  the  effectiveness  of  screening  necessitated  by  the 
abundance  of  non-malarial  mosquitoes.  Three  to  five  grains  of 
quinine  daily,  or  ten  to  fifteen  grains  once  a  week,  is  an  almost 
certain  malaria  preventive.  Quinine,  however,  is  apt  to  cause 
abortion  in  pregnant  women,  though  less  so  than  is  a  severe 
attack  of  malaria.  Some  people  are  naturally  very  susceptible 
to  quinine  and  cannot  take  it;  such  people  should  carefully 
avoid  malarial  districts.  Tea,  coffee  and  other  mild  stimulants 
are  also  said  to  be  beneficial,  but  the  safest  course  is  always  the 
same  —  quinine. 


CHAPTER  X 

OTHER  SPOROZOA,  AND  OBSCURE  OR  INVISIBLE 
PARASITES 

Although  the  class  Sporozoa  includes  a  very  large  number  of 
species,  all  of  which  are  parasitic,  and  many  of  them  the  cause  of 
fatal  diseases  in  vertebrate  as  well  as  invertebrate  animals,  yet 
very  few  other  than  the  malaria  parasites,  already  discussed, 
are  normally  parasitic  in  man,  and  none  of  these  can  be  looked 
upon  as  of  prime  importance  in  the  causation  of  human  disease. 
Of  greatest  importance,  perhaps,  are  the  Coccidiida  or  coccidians, 
which  in  lower  animals  are  frequently  the  cause  of  fatal  diseases 
and  have  been  known  to  be  fatal  to  man,  though  in  some  cases 
causing  very  little  inconvenience.  Another  sporozoan  parasite 
which  is  of  importance  where  it  occurs  is  Rhinosporidium,  which 
produces  tumors  in  the  nose.  A  group  of  muscle-dwelling 
Sporozoa,  the  Sarcosporidia,  occur  accidentally  or  sporadically 
in  man. 

There  is  another  group  of  Sporozoa,  the  Piroplasmata,  related 
to  the  malaria  parasites,  which  are  the  cause  of  some  of  the  most 
fatal  diseases  of  domestic  animals,  including  Texas  fever  and  East 
Coast  fever  of  cattle,  biliary  fever  of  horses,  etc.  These  diseases 
are  invariably,  as  far  as  known,  transmitted  by  ticks.  There  is 
one  human  parasite,  Bartonella  hacilliformis,  the  cause  of  Oroya 
fever  of  Peru,  which  is  thought  to  belong  to  this  group  of  organ- 
isms. Possibly  the  Rickettsia-like  organisms  of  typhus,  trench 
fever,  Rocky  Mountain  spotted  fever,  and  the  related  Japanese 
disease,  kedani,  are  related  to  the  Piroplasmata. 

There  are  a  number  of  other  diseases,  some  of  them  of  great 
importance,  of  which  the  "  germ  "  either  has  never  been  seen  or  is 
of  obscure  nature.  It  is  not  always  possible  to  guess  at  the 
nature  of  such  undiscovered  parasites  but  in  some  cases  we  can 
get  a  fairly  accurate  conception  of  them  from  a  study  of  the  course 
of  the  diseases  they  cause,  the  conditions  under  which  they  thrive 
and  their  means  of  dissemination.     One  by  one  the  villains  be- 

168 


OBSCURE  AND  INVISIBLE  PARASITES  169 

hind  the  screens  are  brought  to  hght,  experimented  with,  and 
brought  under  control  but  there  are  still  some  which  have  defied 
the  most  ardent  researches  of  modern  science  and  have  never  yet 
been  discovered.  The  fact  that  many  of  them  are  able  to  pass 
through  filters  of  certain  kinds,  as  shown  by  the  infectiveness  of 
fluids  containing  them  after  having  been  passed  through  the 
filters,  demonstrates  that  at  least  in  some  stages  of  their  de- 
velopment they  are  actually  too  small  to  be  visible  under  the 
highest  power  of  the  microscope. 

However,  in  the  case  of  some  of  these  unseen  parasites  we  have 
suflicient  knowledge  of  their  habits  and  life  histories  to  wage  a 
fairly  intelligent  war  against  them,  at  least  as  regards  prevention. 
The  parasite  of  yellow  fever,  for  instance,  was  not  discovered 
until  1918.  Yet  we  knew  much  about  its  probable  nature,  we 
knew  its  full  life  history  in  a  general  way,  and  to  a  large  extent 
we  knew  how  to  combat  it,  far  better,  in  fact,  than  we  know  how 
to  combat  some  of  the  well-known  parasites.  There  are  two 
other  diseases,  dengue  and  phlebotomus  fever,  which  are  prob- 
ably caused  by  parasites  related  to  that  of  yellow  fever,  but  they 
have  not  yet  been  discovered. 

The  organisms  of  typhus  fever,  trench  fever,  spotted  fever 
and  kedani  have  only  recently  been  discovered.  They  are  all 
minute  bodies  showing  various  morphological  types,  which  occur 
in  both  vertebrate  and  arthropod  hosts.  They  are  here  grouped 
together  as  "  Rickettsia-like  organisms."  Their  affinities,  whether 
with  bacteria  or  protozoa,  are  at  present  entirely  problematical, 
but  for  the  present  they  may  best  be  considered,  like  the  spiro- 
chsetes,  to  represent  a  more  or  less  intermediate  group. 

Several  other  diseases,  some  of  them  of  prime  importance,  of 
which  the  parasites  are  of  obscure  nature,  are  believed  by  some 
workers  to  be  caused  by  Protozoa:  such  are  hydrophobia  or 
rabies,  trachoma,  smallpox,  verruga  peruviana  (not  Oroya  fever), 
foot-and-mouth  disease,  measles,  scarlet  fever  and  a  few  others. 
The  parasites  or  parasite-like  bodies  which  are  associated 
with  these  diseases  are  in  some  cases  minute,  in  other  cases, 
e.g.,  hydrophobia,  of  relatively  large  size.  In  most  of  these 
diseases  the  "  germ  "  or  virus  is  capable  of  passing  through 
ordinary  bacterial  filters,  as  shown  by  the  infectiveness  of  filtered 
material.     It  is  also  evident  from  this  that  the  viruses  live  out- 


170  OTHER  SPOROZOA 

side  the  cells  or  blood  corpuscles,  at  least  during  part  of  their 
life  history.  On  the  other  hand,  in  these  diseases  there  have 
been  discovered  bodies  of  various  kinds  within  the  cells,  inter- 
preted by  some  workers  as  true  parasites,  by  others  as  reaction 
products  of  the  cells.  These  bodies  have  received  zoological 
names,  e.g.,  the  Negri  bodies  of  hydrophobia  were  named  Neuro- 
ryctes  hydrophohiw,  the  cell  inclusions  in  smallpox  Cytorydes 
variolce,  and  so  on.  It  is  now  a  commoner  belief  that  these  bodies 
consist  of  material  extruded  from  the  nucleus  of  the  cell  into  its 
cytoplasm  where  it  surrounds  one  or  many  of  the  minute  or- 
ganisms during  the  intracellular  portion  of  their  life  history. 

For  these  problematical  organisms,  minute  in  size,  of  uncertam 
life  history,  and  apparently  enshrouded  in  a  mantle  of  extruded 
nuclear  material  during  their  intracellular  life,  the  name  Chlamy- 
dozoa  (meaning  mantle  animals)  has  been  given.  Whether  these 
bodies  have  been  correctly  interpreted  as  described  above  and 
whether  they  should  be  considered  Protozoa  is  open  to  question. 
Their  animal  nature  has  not  been  sufficiently  demonstrated  to 
warrant  more  than  brief  mention  of  them  and  the  diseases  they 
cause  in  a  treatise  on  animal  parasites. 

In  the  following  paragraphs  the  sporozoan  parasites  and  ob- 
scure or  invisible  parasites  which  have  been  briefly  mentioned 
above  will  be  discussed  in  a  little  more  detail  in  the  following 
order:  (1)  coccidians,  (2)  Rhinosporidium,  (3)  Sarcosporidia, 
(4)  Oroya  fever,  (5j  dengue  and  phlebotomus  fever,  (Uj  Rickettsia- 
like  organisms,  (7)  Chlamydozoa. 

Coccidians 

There  are  a  number  of  serious  diseases  of  animals  which  are 
caused  by  parasites  of  the  class  Sporozoa  known  as  coccidians. 
These  are  very  small  animals,  without  distinct  organs  of  lo- 
comotion, which  have  both  an  asexual  and  a  sexual  phase  in 
their  life  history  (Fig.  48).  The  asexual  phase  is  not  unlike 
what  takes  place  in  the  asexual  phase  of  malaria  parasites,  ex- 
cept that  the  parasites  live  inside  of  cells  lining  the  intestine 
instead  of  in  the  blood.  Like  the  malaria  parasites,  a  coccidian, 
within  the  epithehal  cell  in  which  it  is  living  (Fig.  48A-C),  di- 
vides into  two,  four,  eight,  sixteen,  or  perhaps  twenty  or  more 
daughter  cells,  arranged  somewhat  like  the  segments  of  an 
orange  (Fig.  48D).     The  young  coccidians,  escaping  from  the 


COCCIDIANS 


171 


host  cell  which  has  been  preyed  upon  and  destroyed,  invade  fresh 
cells,  multiply  again,  and  thus  eventually  destroy  large  portions 
of  the  lining  of  the  digestive  tract.  The  daughter  coccidians 
are  not  adapted  for  withstanding  conditions  outside  the  intestine 


Fig.  48.  Life  history  of  Eimeria  avium.  A,  infection  of  epithelial  cells  of  in- 
testine by  sporozoites  ingested  with  food  or  water;  B,  growth  inside  cell;  C  and  D, 
sporulation  and  formation  of  young  spores;  E  and  G,  formation  of  female  gamete; 
F  and  H,  formation  of  male  gametes;  /,  fertilization;  J,  fully  developed  oocyst  as 
passed  out  with  faeces;  K,  L  and  M,  formation  of  four  sporocysts;  N,  complete 
development  of  sporocysts,  each  containing  two  sporozoites;  O,  same,  ingested  by 
susceptible  animal;  P,  sporocyst  liberated  from  oocyst  in  alimentary  canal;  Q, 
liberated  sporozoite  ready  to  infect  epithelial  cell,  as  shown  in  A. 

of  the  host,  and  therefore  the  parasite  would  be  exterminated 
with  the  death  of  its  host  were  it  not  protected  in  some  manner 
against  this  calamity.     The  sexual  phase  of  its  life  history  serves 


172  OTHER  SPOROZOA 

this  important  purpose.  At  intervals  the  coccidians,  instead 
of  multiplying  in  the  usual  manner,  differentiate  into  sexual  forms, 
corresponding  to  eggs  and  sperms  (Fig.  48G  and  H).  One  of  the 
spermlike  individuals  penetrates  an  egglike  individual  and  fuses 
with  it  (Fig.  481),  in  precisely  the  same  manner  as  a  spermatozoon 
fertilizes  an  egg  in  higher  animals.  The  fertihzed  individual 
develops  a  thick  resistant  cyst  wall  and  is  then  known  as  an 
'^  oocyst"  (Fig.  48J)l  The  parasite  is  now  ready  to  hazard  the 
dangers  of  an  exit  into  the  outside  world,  and  is  passed  out  with 
the  faeces.  Eventually,  sometimes  within  a  few  days,  the  con- 
tents of  the  oocyst  divide  into  several  parts,  each  known  as  a 
''  sporocyst  "  (Fig.  48K,  L  and  M).  Each  sporocyst  in  turn 
develops  within  itself  a  number  of  "  sporozoites  "  (Fig.  48N), 
each  capable  of  infecting  a  separate  cell 
in  a  new  host.  The  oocysts  with  their 
contained  sporocysts  and  sporozoites  can 
exist  in  soil  or  dust  for  a  long  time, 
awaiting  an  opportunity  to  enter  a  new 
Fig.  49.  Oocyst  of  iso-  victim  with  food  or  water. 
spora  from  British  soldier       Infection  with  coccidians  has  not  often 

returned      from      Gallipoli.    i  v  i     •  i_    j.      -i      • 

Note  presence  of  only  two  ^een    observed    m    man   but    it    IS    pos- 
sporocysts,  each  with  four  sibly  more  prevalent  than   is  commonly 

sporozoites.    X  1000.   (After    ii  i  j.         a    r  r  '  t         •    r 

Wenyon.)  thought.     A  fcw  cases  01  coccidian  infec- 

tion of  the  human  liver  have  been  recorded 
and  it  has  been  generally  assumed  that  the  parasite  was  identical 
with  Eimeria  stiedce  of  rabbits,  but  Dobell  has  pointed  out  that 
there  is  no  sound  reason  for  this  belief.  Recently  Wenyon  has 
reported  the  not  uncommon  occurrence  of  oocysts  of  two  species 
of  coccidians  in  the  faeces  of  British  soldiers  returning  from  Gal- 
lipoli. The  cysts  of  the  commoner  species,  Isospora  hominis, 
contain  a  single  mass  of  protoplasm,  when  first  passed,  but  in  three 
or  four  days  they  become  fully  developed  and  contain  two  sporo- 
cysts, each  with  four  sporozoites  (Fig.  49).  The  cysts  measure 
12  M  to  14  At  by  7  M  to  9  M  (about  -j^Vo  by  ^oVo  of  ^^  inch).  The 
cysts  of  the  other  species,  Eimeria  wenyoni,  are  fully  developed 
when  passed,  and  possess  four  sporocysts  with  two  sporozoites 
each  (Fig.  50)  They  measure  20  /x  in  diameter.  Only  four 
cases  of  infection  are  known.  A  single  case  each  of  infection  with 
two  other  species  have  been  recorded:  E.  oxy spora,  with  large 
spherical  cysts  (36  fx  in  diameter)  and  straight  sharp-pointed 
spores,  recorded  by  Dobell;    and  E.  snijderi,  with   still   larger 


RHINOSPORIDIUM 


173 


Sporocyot 
Sporozolte 


cysts  but  smaller  spores,  by  Snijder  in  Sumatra.     Little  is  known 
of  the  symptoms  produced  by  these  parasites,  but  since  they  live 
inside  epithelial  cells  of  the  intestine  or  liver  they  must  be  in- 
jurious.    Wenyon  has  recently  reported 
dysenteric  symptoms  in  a  case  in  which 

no  intestinal  parasites  except  Isospora     / //MIW    \ oocyst 

were  present.  Coccidians  are  un- 
doubtedly spread  by  means  of  water 
or  food  polluted  by  mud  and  dirt,  by  un- 
sanitary habits,  and  by  flies. 

Rhinosporidiuniy  a  Parasite  of  the 
Nose 
In  natives  of  India  there  is  occasion-       ^^^-.^^   Oocyst  of  ^tmerio 

.  containing  four  sporocysts,  each 

ally  observed  a  peculiar  mfection  of  the  with  two  sporozoites. 
nose  in  which  a  red  tumor,  flecked  with 

whitish  spots,  and  likened  by  some  authors  to  a  raspberry,  grows 
out  from  the  partition  or  septum  of  the  nose,  remaining  attached 
by  a  narrow  stalk.  The  tumors  are  not  very  painful,  but  they 
tend  to  block  the  nasal  passages.  It  has  been  suggested  that 
this  disease,  kjiown  as  nasal  polypus,  may  have  the  same  in- 
fluence on  the  intellect  of  children  that  o  her  impediments  of 
the  nose  and  throat  are  known  to  have. 

When  the  tumor  is  cut  the  white  spots  visible  on  the  surface 
are  seen  to  be  scattered  throughout  the  tissue  and  to  be  of  very 
variable  size.  Microscopic  examination  shows  them  to  be  the 
cysts  of  a  protozoan  parasite  in  various  stages  of  development. 
The  parasite  has  been  named  Rhinospo  idium  kinealyi,  and  is 
classified  as  a  member  of  the  group  of  Sporozoa  known  as  Haplo- 
sporidia. 

The  cysts  in  the  tumor  are  filled  with  great  numbers  of  spherical 
or  oval  bodies,  the  pansporoblasts,  each  of  these  in  turn  contain- 
ing from  one  to  a  dozen  closely-packed  spores  (see  small  portion 
of  a  cyst  in  Fig.  51).  The  manner  of  development  of  the  cysts 
and  of  the  tumor  can  readily  be  discovered  from  the  various 
stages  of  development  of  different  cysts  and  parts  of  cysts  which 
can  be  observed  in  a  single  tumor.  The  youngest  cysts  are  small 
granular  masses  of  protoplasm,  more  or  less  irregular  in  shape. 
As  one  of  these  minute  animals  grows  there  are  developed  within 
it  small  bodies  with  definite  shape  which  are  destined  to  become 
the    pansporoblasts    already    mentioned.     However,    the  proto- 


174  OTHER  SPOROZOA 

plasm  at  the  periphery  of  the  animal  continues  to  grow,  constantly 
becoming  differentiated  into  new  pansporoblasts.  The  young 
pansporoblasts  (Fig.  51,  yg.  pansp.),  at  first  simple  masses  of 
protoplasm,  soon  form  within  themselves  one,  two,  four,  and 
ultimately  as  many  as  12  spores,  tightly  clumped  together  so 

as  to  resemble  little  mul- 

(»ysf, — ^^g^;=~  ^^^^^^^^^^^^^      berries     (Fig.     51,     mat. 

_  pansp.).     From  the  mode 

c,g.  pansp.  ^^^^^^^  of    development    of    the 

cysts  it  is  clear  that  the 
older  pansporoblasts  are 
the  ones  near  the  center 
of  the  cyst,  the  younger 
ones    those    toward    the 

rrictt  pansp. ^^i^^^^lf  periphery.        When     the 

" '    "  cysts     have     reached     a 

^p ""ii^^l^^^ii^S^  certain    size    the    growth 

of  the  periphery  ceases, 
all  the  pansporoblasts  ma- 

FiG.  51.     Portion  of  fully  developed  cyst  of  ,  j  xi,  x  x 

Rhinosporidium;   c.   w.,   cyst  wall;    yg.   pansp.,  ture  and  the  Cyst  ruptureS, 

young  pansporoblasts;    mat.   pansp.,    fully    de-  liberating  the   SporeS   into 

veloped  pansporoblasts    containing    spores,    sp.  ,i  j.  ,• 

X  about  100.     (After  Fantham  and  Porter.)  ^he      SUrrOUndmg      tlSSUe, 

each  to  develop  into  a 
new  cyst.  How  the  parasites  are  transmitted  to  new  hosts  is 
not  known. 

A  similar  disease  was  found  some  years  ago  in  South  America 
and  a  parasite,  then  named  Coccidium  seeberi,  has  been  described 
from  the  tumors.  It  is  possible  that  this  may  be  the  same 
organism  as  that  of  Indian  nasal  polypus,  but  according  to  Fan- 
tham, who  was  one  of  the  original  describers  of  Rhinosporidium, 
there  are  a  number  of  differences  between  them. 


Sarcosporidia,  Parasites  of  the  Muscles 

Brief  mention  should  be  made  of  a  group  of  Sporozoa  known 
as  the  Sarcosporidia  which  develop  relatively  enormous  cysts 
in  the  muscles  of  vertebrate  animals,  especially  in  mammals. 
These  parasites  are  usually  found  in  the  striped  muscles  but  they 
also  occur  in  other  muscles.  Infected  muscles  (Fig.  52B  and  D) 
appear  to   have  white  streaks  or  patches  in  them,  sometimes 


SARCOSPORIDIA 


175 


several  inches  in  length.  Microscopic  examination  shows  that 
these  patches  are  cysts  containing  thousands  of  tiny  spores, 
segregated  into  chambers  (Fig.  52A)  which  correspond  to  the 
pansporoblasts  of  Rhinosporidium.  The  spores  (Fig.  52C),  es- 
caping from  the  cyst,  ultimately  develop  into  new  cysts  in  much 


D 

Fig.  52.  Sarcosporidia.  A,  Sarcocystis  blanchardi  of  ox,  longitudinal  section  of 
infected  muscle  fiber  (m.  f.)  showing  spores  (sp.)  in  chambers  of  compartments 
(comp.);  n.,  nucleus  of  muscle  fiber,  X  265.  (After  von  Eecke  from  Wasilewsky.) 
B,  cross  section  of  sarcocyst  from  human  larynx,  probably  S.  tenella,  X  200.  D, 
same,  longitudinal  section.  (After  Baraban  and  St.  Remy.)  C,  spore  of  S.  tenella 
of  sheep.      (After  Laveran  and  Mesnil.) 


the  same  way  as  is  the  case  with  the  nose  parasite.  Although 
the  muscle  parasites  have  been  known  to  parasitologists  for 
many  years  there  are  portions  of  the  life  history  which  are  not 
yet  known.  Darling  and  others  have  suggested  that  these  pe- 
culiar protozoans  may  be  "  side-tracked  varieties  of  parasites  of 
invertebrate  animals."  We  have  no  definite  knowledge  of  the 
normal  means  of  transmission  although  a  number  of  possible 
methods  are  known.  It  has  been  found  that  infections  can  be 
spread  by  cannibalism,  and  that  the  faeces  of  infected  mice  can 
infect  other  mice;  it  has  also  been  stated  that  spores  occur  in 
the  circulating  blood,  which  would  mean  that  blood-sucking  ar- 
thropods may  be  instrumental  in  the  transfer.  Fleshflies  may 
also  play  a  part  in  dispersing  the  spores.  • 

Erdmann  has  shown  that  when  spores  of  Sarcosporidia  de- 
velop in  the  intestine  a  very  powerful  toxin,  called  sarcocystin, 
is  discharged  and  destroys  the  neighboring  epithelial  cells  of  the 
intestine  and  thus  breaks  a  way  for  the  young  parasite  into  the 


176  OTHER  SPOROZOA 

lymphatics  and  ultimately  into  the  muscles.  Crawley  has  re- 
cently described  in  Sarcocystis  muris  of  mice  what  he  interprets 
as  sexual  differentiation  of  the  spores  and  fertilization  within 
18  hours  after  the  spores  have  been  ingested  by  mice.  Crawley 
beheves  the  Sarcosporidia  to  be  closely  aUied  to  the  Coccidia,  and 
suggests  that  there  may  be  an  unrecognized  stage  of  development 
in  a  carnivorous  animal.  It  is  quite  evident  from  the  various 
hypotheses  and  speculations  mentioned  above  that  there  is  much 
yet  to  be  learned  about  these  enigmatic  parasites. 

Only  a  few  scattered  cases  of  Sarcosporidia  in  man  have  been 
recorded,  and  these  may  be  looked  upon  as  purely  accidental. 
The  parts  affected  have  been  the  muscles  of  the  heart  and  larynx. 
Many  speculations  as  to  how  these  infections  occurred  have  been 
made,  but  nothing  definite  is  known  about  it.  It  is  probable 
that  the  human  infections  are  due  to  Sarcocystis  muris,  a  species 
which  produces  a  very  fatal  disease  in  mice,  and  infections  may 
have  been  due  to  contamination  of  food  or  water  with  the  ex- 
crement of  infected  mice.  The  use  of  meat  of  Indian  buffaloes 
infected  with  another  species,  Sarcocystis  tenella  huhali,  seems  to 
have  no  injurious  effect  on  man,  but  ingested  spores  cause  ir- 
regular fever. 

Oroya  Fever 

The  Disease.  —  Since  at  least  the  time  of  the  Incas,  Peru  has 
suffered  from  a  strange  disease  which  has  swept  over  the  country 
from  time  to  time  in  the  form  of  frightful  epidemics,  some  of 
which  have  cost  thousands  of  lives.  One  of  the  severest  recent 
outbreaks  occurred  among  the  workmen  building  the  Peruvian 
Central  Railway  between  Lima  and  Oroya  and  it  is  estimated 
that  at  least  7000  individuals  died  in  it.  In  1906  at  least  one- 
tenth  of  2000  workmen  employed  building  tunnels  and  bridges 
on  the  Central  Railway  died  of  the  fever,  and  one  bridge  in  par- 
ticular, which  was  the  scene  of  a  great  many  deaths  from  the  dis- 
ease, has  come  to  be  known  as  the  Oroya  Fever  Bridge  (Fig.  53). 

The  disease  is  at  present  endemic  in  the  deep  cleft  canyons  or 
quehradas  (Fig.  53)  characteristic  of  the  west  face  of  the  Andes,  at 
an  elevation  of  between  2500  and  8000  ft.,  but  it  is  probable  that  it 
has  a  wider  distribution  than  is  now  supposed.  It  shows  a  marked 
seasonal  prevalence,  most  of  the  cases  occurring  from  January  to 
April,  especially  toward  the  close  of  the  warm,  rainy  season. 


OROYA  FEVER 


177 


Fig.  53*  Above,  a  typical  "  quebrada  "  or  canyon  on  the  west  slopB  of  the  Andes 
Where  Oroya  fever  abounds.  Below,  the  famous  "Oroya  Fever  Bridge "  on  Peruvian 
Central  Railway  where  hundreds  of  lives  were  lost  from  Oroya  fever.  (Photos 
kindly  lent  by  Harvard  School  of  Tropical  Medicine,  previously  published  by 
Strong  et  aX>.) 


178  OTHER  SFOROZOA 

Oroya  fever  has  been  constantly  confused  with  other  diseases; 
and  it  was  not  until  the  South  American  expedition  of  the 
Harvard  School  of  Tropical  Medicine,  under  the  leadership  of 
Dr.  R.  P.  Strong,  made  an  investigation  of  the  disease  that 
soine  order  was  brought  out  of  the  confusion.  Malaria,  para- 
typhoid, and  particularly  verruga  peruviana  are  the  diseases 
which  have  been  most  frequently  confused  with  Oroya  fever. 
Mixed  infection  of  these  diseases  and  others  such  as  yaws  and 
tuberculosis  with  true  Oroya  fever  has  still  further  complicated 
matters.  From  the  time  of  the  Incas  verruga  peruviana  and 
Oroya  fever  have  been  associated  and  regarded  as  different  phases 
of  the  same  disease,  and  this  view  is  still  held  by  some  investi- 
gators. The  fact  that  the  characteristic  nodules  of  verruga  were 
usually  associated  with  a  very  mild  form  of  fever  and  sometimes 
with  none  at  all,  while  oroya  fever  was  of  very  severe  type  caus- 
ing very  high  fatality,  raised  some  question  as  to  the  distinctness 
of  the  diseases.  To  settle  this  point  a  Peruvian  medical  stu- 
dent, Daniel  Carrion,  vaccinated  himself  with  blood  from  a 
verruga  nodule.  Five  or  six  weeks  later  he  died  of  a  severe 
fever,  and  the  question  of  the  identity  of  the  disease  was  ap- 
parently settled,  and  the  fever  was  called  '^  Carrion's  Fever '' 
in  his  honor.  The  notes  regarding  Carrion's  illness  have  been 
lost  and  it  is  now  believed  that  he  may  have  died  of  some  other 
disease  or  that  the  patient  from  whom  he  inoculated  himself 
may  have  been  suffering  from  some  other  disease  in  addition  to 
verruga. 

As  a  result  of  their  own  studies,  Dr.  Strong  and  his  colleagues 
believe  that  the  diseases  are  quite  distinct.  They  have  shown 
that  Oroya  fever  is  caused  by  a  very  minute  parasite  Kving  in 
the  red  blood  corpuscles  and  multiplying  in  the  endothelial  cells, 
and  that  it  cannot  be  inoculated  into  animals ;  verruga  peruviana, 
on  the  other  hand,  is  caused  by  a  virus  which  is  ultra-microscopic, 
probably  related  to  the  smallpox  virus,  and  can  be  successfully 
inoculated  into  laboratory  animals.  It  is  easy  to  understand 
how  the  two  diseases  were  confused,  since  to  a  large  extent  their 
ranges  overlap  and  a  visitor  to  endemic  regions  would  be  likely 
to  contract  both.  Verruga,  being  less  quickly  contracted  and 
having  a  longer  incubation  period,  would  tend  to  appear  later 
than  Oroya  fever,  and  would  therefore  be  looked  upon  as  a  later 
stage  of  the  same  disease.     The  native  belief  that  a  general  erup- 


BARTONELLA  BACILLIFORMIS 


179 


tion  was  favorable  to  recovery,  a  belief  undoubtedly  based  upon 
the  benign  nature  of  verruga,  leads  to  the  adoption  of  all  sorts  of 
methods  to  invoke  a  breaking  out  of  the  skin,  such  as  applications 
of  turpentine,  rubbing  with  irritant  leaves,  etc.,  and  undoubtedly 
a  great  many  cases  of  eruptions  following  Oioya  fever  are  really 
only  the  eruptions  caused  by  the  artificial  irritation  of  the  skin. 

Oroya  fever,  after  an  incubation  period  of  about  20  days,  begins 
with  a  general  feeling  of  malaise  and  aches  in  the  joints,  followed 
by  chills  and  fever,  which  last  irregularly  for  many  weeks.  The 
fever  is  accompanied  by  a  rapid  pernicious  anemia,  the  red  blood 
corpuscles  being  reduced  in  some  cases  to  one-fifth,  or  even  less, 
of  their  normal  number.  This  causes  severe  prostration  and 
in  a  large  per  cent  of  cases  death  results  within  three  or  four 
weeks.  The  skin  assumes  a  yellowish  waxy  color,  and  there  are 
often  slight  hemorrhages  of  the  mucous  membranes  and  various 
internal  organs,  as  demonstrated  by  post  mortem  examinations. 
The  liver  and  spleen  become  moderately  enlarged,  and  the  lymph 
glands  are  swollen. 

The  Parasite.  —  The  true  parasite  of  Oroya  fever  was  first 
discovered  by  Barton,  of  Lima,  Peru,  in  1905  and  confirmed  by 
him  in  1909,  at  which  time  he 
suspected  that  it  might  be  a 
protozoan.  The  parasites  were 
more  thoroughly  studied  by 
the  Harvard  expedition  in  1913 
and  1914  and  named  Barton- 
ella hadlliformis.  Dr.  Strong 
and     his     colleagues     describe 

them   as   minute  rods  or,    more  Fig.  54.     Bartonella  badUiformis,  liv- 

1                   rl   rl    K    rl'  ^^^"     ^'  -^  ^^^  ^'  successive  drawings  of 

rarely,     rOUndea    DOClieS    occur-  ^  single  red  corpuscle  showing  movements 

ring   inside   the    red    blood    cor-  of  parasite  within  it ;  Z),£^  and  F,  corpuscle 

1           <"t?'            'A           r\       KK\  containing  two  rod-shaped  and  four  round 

pUSCleS      (l^lgS.      04      ana      OO;.  parasites,  showing  migrations  of  the  rod- 

These  parasites,  the  rod  form  shaped  individuals.  x  2000.  (After 
of  which  are  only  1.5  to  2.5  /a      ^^^^  ^ 

(less  than  ^  ^  ^^  ^  ^  of  an  inch)  in  length  and  the  round  bodies  0.5  to 
1  fjL  in  diameter,  are  definitely  motile,  moving  about  freely  inside 
the  corpuscles.  In  severe  infections  there  may  be  found  from 
one  to  ten  parasites  in  a  single  corpuscle. 

A  multiplicative  stage  of  the  parasite  occurs  in  large  swollen 
endothelial  cells  in  the  lymph  glands  and  spleen.     In  these  swollen 


180 


OTHER  SPOROZOA 


Fig.  55.  Bartonella  hacillifonnis  in  stained  blood 
from  Oroya  fever  patient.  Some  cells  show  chains  of 
parasites.  Bodies  v  ith  large  dark  nuclei  are  leuco- 
cytes (leuc).    X  about  1000.     (After  Strong  et  al.) 


Fig.  56.  Development  of  Bartonella  bacilliformis 
in  endothelial  cells.  A,  endothelial  cell,  with  large 
nucleus  (n.)  at  left,  containing  five  rounded  bodies  in 
early  stage  of  development;  B,  endothelial  cell  show- 
ing rounded  bodies  developing  large  numbers  of  small 
rod-shaped  parasites;  C,  red  corpuscles  lying  near 
with  parasites  identical  with  those  escaping  from  such 


cells  are  mitiut^ 
rounded  bodies,  some- 
times a  few,  some- 
times great  masses  of 
them  (Fig.  56B)- 
Some  of  these  rounded 
bodies  contain  only 
one,  two  or  four  deep 
staining  granules 
(Fig.  56A),  while 
others  contain  large 
numbers  of  them. 
It  appears  that  these 
granule  -  filled  bodies 
break  up  into  a  large 
number  of  parts  each 
containing  one  gran- 
ule; these  become 
elongated,  and  finally 
appear  as  distinct  rods 
containing  the  gran- 
ule at  one  end.  In 
this  condition  they 
are  identical  with  the 
parasites  which  occur 
in  the  red  blood  cor- 
puscles (Fig.  56C)  and 
indicate  the  manner 
in  which  the  corpus- 
cular parasites  arise. 
Dr.  Strong  and  his 
colleagues  believe 
Bartonella  bacilli-' 
for  mis  to  be  a  pro- 
tozoan   probably    re- 


;e  escaping  irom  sucn    i    ,      i   j.       +v>         ♦>  f 

a  cell  as  shown  in  B.      X  2000.     (After  Strong  et  al.)    ^^^^^  ^^   ^^^  grOUp  01 

parasites  known  as 
the  Piroplasmata,  including  the  Texas  fever  parasite  of  cattle  and 
a  number  of  other  disease-causing  parasites  of  wild  and  domestic 
animals.     Its  exact  classification  cannot  yet  be  determined,  and 


TRANSMISSION  OF  OROYA   FEVER  181 

it  is  simply  looked  upon  as  possibly  belonging  to  a  group  of  micro- 
organisms intermediate,  as  perhaps  are  the  spirochaetes,  between 
Bacteria  and  Protozoa,  but  with  a  decided  leaning  toward  the 
latter.     Possibly  they  are  related  to  Rickettsia.     (See  p.  185.) 

Transmission.  —  The  method  of  transmission  of  Oroya  fever 
is  still  in  doubt,  but  it  seems  practically  certain  that  some  ar- 
thropod acts  as  a  transmitting  agent.  All  the  other  parasites 
of  the  group  to  which  Bartonella  belongs  are  transmitted  by  ticks, 
but  there  is  apparently  no  tick  having  habits  compatible  with  the 
occurrence  of  the  disease.  The  Harvard  expedition  attempted 
to  obtain  the  development  of  Bartonella  in  a  mosquito,  Pha- 
langomyia  dehilis,  which  is  common  in  the  infected  zones,  but 
without  success.  That  the  transmitting  agent  is  a  nocturnal 
blood-sucker  of  very  limited  distribution  but  abundant  within 
its  range  is  strongly  indicated  by  the  limitations  of  the  disease 
and  by  the  fact  that  in  many  cases  a  single  night  in  the  infected 
zone  is  suificient  for  contracting  it,  whereas  there  is  apparently 
no  danger  a  short  distance  from  the  infected  zone,  or  within  it 
in  the  daytime.  According  to  Townsend,  who  spent  two  years 
investigating  verruga  (which  he  considers  identical  with  Oroya 
fever)  the  only  arthropod  which  fulfills  all  the  conditions  is  a 
sandfly,  Phlebotomus  verrucarum,  which  is  a  very  abundant 
nocturnal  blood-sucker  apparently  limited  in  its  distribution  to 
the  verruga  zones.  Townsend  attempted  experiments  with  the 
transmission  of  the  disease  through  the  agency  of  this  insect  but 
his  results  have  not  been  generally  accepted.  Whether  or  not 
Phlebotomus  is  instrumental  in  transmitting  Oroya  fever  is  a 
matter  which  will  have  to  be  proved  by  further  research  but  the 
circumstantial  evidence  against  the  insect  is  strong. 

As  pointed  out  by  Townsend,  the  portions  of  Peru  which  are 
haunted  by  Oroya  fever  and  verruga  have  one  of  the  most  perfect 
and  healthful  climates  in  the  world  and  they  would  be  ideal  for 
sanatoriums  and  resorts  were  it  not  for  these  diseases.  It  is  to 
be  hoped  that  the  diseases  may  soon  be  more  thoroughly  worked 
out  and  gotten  under  control.  However,  if  Phlebotomus  is  in- 
strumental in  the  transmission  of  either,  the  hope  of  eradicating 
them  in  the  near  future  is  slight,  judging  by  the  difficulties  which 
have  been  experienced  in  Mediterranean  countries  in  controlling 
these  minute  rock-breeding  insects. 


182  OTHER  SPOROZOA 

Dengue  and  Phlebotomus  Fever 

These  two  diseases  are  wide-spread  in  tropical  and  subtropical 
countries,  and  are  frequently  confused.  They  have  commonly 
been  associated  with  yellow  fever,  none  of  the  parasites  causing 
them  having  been  discovered  until  Noguchi  discovered  a*  Lep- 
tospira as  the  causative  organism  of  yellow  fever  in  1918.  It  is 
possible  that  the  other  two  diseases  will  also  be  shown  to  be 
caused  by  species  of  Leptospira.  Dengue  is  a  much  milder  disease 
than  yellow  fever  and  is  seldom  fatal,  though  its  after-effects 
linger  for  many  months.  Phlebotomus  or  three-days'  fever  is  a 
still  milder  disease  and,  as  its  name  implies,  of  short  duration. 
Like  dengue  it  has  lingering  after-effects  but  they  are  not  so  severe 
or  so  persistent  as  in  the  former  disease. 

Both  diseases  are  caused  by  blood  parasites,  so  far  undiscovered, 
which  are  transmitted  by  dipterous  insects  in  which  they  ap- 
parently undergo  part  of  their  life  cycle.  The  diseases  each  begin 
with  a  sudden  high  fever  and  headache,  and  pass  through  es- 
sentially similar  stages,  intense  rheumatism-like  aches  being  very 
characteristic  of  all.  Each  disease  confers  immunity,  often  of 
long  duration  in  dengue  and  often  transitory  in  phlebotomus 
fever.  It  seems  not  improbable  that  the  parasites  of  these  dis- 
eases and  of  yellow  fever  are  closely  allied- 
Dengue 

Dengue,  seven-days'  fever,  or  breakbone  fever,  is  a  disease  of 
tropical  and  subtropical  countries.  It  is  very  common  in  the 
West  Indies  and  great  epidemics  have  swept  through  Panama, 
the  eastern  Mediterranean  and  southern  Asian  countries,  the 
Philippine  Islands  and  various  South  Sea  Islands.  An  epidemic 
has  recently  been  reported  from  Argentina  and  Uruguay,  the  dis- 
ease supposedly  having  been  introduced  from  Spain,  Dengue  also 
occurs  in  southern  United  States  where  it  is  probably  often  over- 
looked, being  diagnosed  as  something  else.  In  some  places,  e.g., 
southeastern  Europe  and  India,  there  is  some  confusion  between 
dengue  and  phlebotomus  fever.  Both  diseases  vary  somewhat 
and  mild  types  of  the  former  and  severe  types  of  the  latter  may 
easily  be,  and  frequently  are,  confused.  Dengue  occurs  in  the 
form  of  sudden  and  rapidly  spreading  epidemics  which  sweep 


DENGUE  183 

over  limited  areas,  affecting  a  large  per  cent  of  the  popu- 
lation. 

Nearly  every  fluid  and  organ  of  the  body  has  been  examined 
in  an  effort  to  find  the  organism  causing  dengue,  but  although 
many  supposed  parasites  have  been  found,  the  true  cause  of  the 
disease  is  still  unknown.  In  at  least  one  stage  of  its  life  history 
the  parasite,  like  that  of  yellow  fever,  is  ultra-microscopic.  The 
disease  has  been  proven  by  experimentation  to  be  transmitted 
commonly  by  the  tropical  house  mosquito,  Culex  quinquefasciatus, 
and  its  distribution  geographically  coincides  very  closely  with 
that  of  this  mosquito.  However,  Aedes  calopus  has  also  been  in- 
criminated, and  in  Formosa  another  closely  related  species, 
Desvoidea  obturhans. 

Unlike  yellow  fever,  dengue  has  a  very  short  incubation  period 
in  the  mosquito  —  in  one  experiment  it  was  only  48  hours.  This 
fact,  together  with  the  short  incubation  period  in  the  human 
body  (from  two  to  five  days),  explains  the  rapidity  with  which 
dengue  epidemics  spread. 

The  disease  begins  with  startling  suddenness.  Within  a  few 
hours  a  normal  healthy  individual  acquires  a  prostrating  fever, 
a  severe  headache  and  terrible  aches  in  the  bones  and  joints 
which  make  it  necessary  to  lie  still.  His  face  and  sometimes 
his  whole  body  becomes  flushed  and  purple  with  congested  blood- 
vessels, and  the  patient  is  to  say  the  least  very  miserable.  In 
a  day  or  two  the  fever  moderates,  and  usually  is  terminated  by 
a  sudden  crisis  of  nose-bleed  and  diarrhea,  relieving  the  con- 
gestion which  has  been  felt  in  all  parts  of  the  body.  Then  follows 
an  interval  of  apparently  normal  condition  during  which  the 
patient  feels  perfectly  well.  After  a  few  days  there  is  a  return  of 
more  or  less  severe  fever  and  aches  accompanied  by  a  measles- 
like rash.  The  latter  fades  in  from  three  to  five  days  and  is  fol- 
lowed by  a  powdery  scaling  off  of  the  skin.  If  lucky,  the  patient 
now  quickly  recovers  but  more  often  he  has  lingering  and  recur- 
ring aches  in  various  joints,  especially  the  knees  and  ankles,  and 
he  may  be  thus  afflicted  for  several  weeks  before  final  recuper- 
ation, whence  the  name  "  breakbone  fever."  The  disease  is 
dangerous  to  life  only  if  complicated  in  some  way. 

An  attack  of  dengue  usually  confers  immunity  on  an  individ- 
ual but  this  sometimes  lasts  only  a  year  and  is  sometimes  not 
established  at  all,  since  more  than  one  attack  during  a  single 
epidemic  have  been  known  to  occur. 


184  OTHER  SPOROZOA 

There  is  no  specific  remedy  known  that  will  cure  dengue. 
Care  of  the  general  health,  including  measures  to  lessen  the  fever, 
headache  and  bone  aches,  help  in  making  life  worth  living  during 
the  eight  or  ten  days  of  suffering. 

Once  an  epidemic  has  broken  out,  it  is  almost  as  useless  to 
attempt  to  stop  it  as  to  stop  a  tidal  wave,  as  far  as  the  mass  of 
people  is  concerned.  Houses  screened  against  mosquitoes,  if 
available,  are  havens  of  refuge,  but  the  tropical  villages  or  cities 
in  which  there  are  enough  screened  houses  to  care  for  even  a 
small  per  cent  of  the  population  are  hopelessly  lacking,  and  the 
rapidity  of  the  spread  of  the  disease  makes  the  isolation  of  early 
cases  in  mosquito-proof  wards  almost  futile.  Anti-mosquito 
campaigns,  conducted  not  merely  during  an  epidemic  but  at  all 
times,  are  the  only  methods  now  known  of  preventing  epidemics 
of  dengue  or  of  lessening  their  local  prevalence. 

Phlebotomus  Fever 

Of  the  same  general  nature  as  yellow  fever  and  dengue,  and 
concluding  this  series  of  gradually  milder  diseases,  is  phlebot- 
omus or  three-days'  fever.  This  disease  occurs  especially  on 
the  shores  of  the  Mediterranean  and  in  India,  and  possibly  also 
in  other  parts  of  the  world.  In  endemic  countries  it  occurs  in 
the  form  of  annual  epidemics.  It  is  estimated  that  in  the  earth- 
quake regions  of  Italy  where  the  disease  is  especially  prevalent, 
50,000  persons  are  attacked  annually,  incurring  a  financial  loss 
of  over  $7,000,000  by  the  prolonged  incapacitation  for  work  which 
follows  the  disease.  In  central  India,  every  non-immune  person 
is  said  to  be  attacked  by  the  end  of  June  each  year. 

Phlebotomus  fever  begins  suddenly,  like  dengue,  with  a  high 
fever,  severe  headache  and  aches  in  the  bones  and  joints.  The 
nervous  symptoms  are  marked,  and  the  pulse  and  respiration  are 
accelerated.  Usually  the  fever  subsides  on  the  third  day,  though 
in  India  it  often  lasts  four  or  five  days.  The  aches  and  general 
depression  continue  for  ten  or  twelve  days  or  even  longer  after 
the  disappearance  of  the  fever. 

The  disease,  the  parasite  of  which  has  never  been  discovered, 
is  transmitted  by  the  gnat  or  sandfly,  Phlebotomus  papatasii 
(see  p.  470,  and  Fig.  212),  which  is  extremely  abundant  in  the 
regions  where  phlebotomus  fever  is  endemic.  The  appearance 
and  habits  of  this  insect  are  described  on  p.  471.     The  prevalence 


RICKETTSIA-LIKE  ORGANISMS  185 

of  phlebotomus  fever  in  the  earthquake  districts  is  due  to  the 
abundance  of  ideal  breeding  places  for  the  gnats  furnished  by 
the  ruined  walls.  It  is  possible  that  other  species  of  Phlebotomus 
may  also  transmit  the  disease. 

The  gnats  become  infective  about  a  week  after  feeding  on  an 
infected  person.  The  incubation  period  of  the  disease  in  man  is 
about  four  or  five  days.  Natural  immunity  is  extremely  rare, 
but  in  most  cases  an  immunity  of  variable  duration  results  from 
an  attack  of  the  disease. 

No  specific  cure  has  yet  been  discovered.  Prevention  lies 
in  avoiding  the  bites  of  Phlebotomus  papatasii  and  in  reducing 
their  numbers  as  far  as  possible  by  methods  described  on  p.  473. 
In  case  of  prolonged  residence  in  an  endemic  region,  there  is 
little  hope  of  escaping  infection,  and  willful  exposure  to  it  at  a 
time  when  the  disease  will  be  least  inconvenient  is  usually  ad- 
visable, in  view  of  the  usually  persistent  immunity  which  results. 

Rickettsia-Like  Organisms 
Within  the  past  few  years  there  have  been  described  as  the 
probable  cause  of  a  number  of  human  diseases,  organisms  of  very 
minute  size,  frequently  less  than  half  a  micron  in  diameter,  which 
may  show  a  number  of  morphological  types.  Round  or  diplococcal 
forms  are  of  most  frequent  occurrence,  but  there  also  occur  minute 
rod-shaped  bodies  and  occasionally  threadlike  forms.  The  re- 
lationships of  these  organisms  is  very  obscure.  They  are  looked 
upon  by  some  investigators  as  bacteria,  and  by  others  as  protozoa, 
while  still  others  consider  them  merely  by-products  of  the  infection. 
In  their  staining  reactions  they  resemble  spirochaetes  rather  than 
bacteria,  and  the  possibility  of  their  representing  modified  granule 
stages  of  spirochaetes  has  been  suggested.  They  are  non-motile, 
and  very  difficult  to  cultivate.  They  occur  in  a  number  of  kinds 
of  arthropods,  usually  multiplying  on  or  in  the  epithelial  cells  of 
the  alimentary  canal,  but  some  species,  at  least,  occur  in  other 
organs  also,  including  the  reproductive  glands,  and  are  hereditarily 
transmitted.  The  resemblance  to  spirochaetes  is  further  borne 
out  by  the  way  in  which  reproduction  takes  place  by  granule- 
shedding  from  elongated  threadlike  forms,  and  by  their  hereditary 
transmission  among  arthropods.  Species  of  Rickettsia  or  closely 
allied  forms  have  been  found  in  human  lice  (Pediculus),  Mal- 
lophaga,  fleas,  bugs  {Cimex),  sheep  ticks  (Melophagus),  and  true 


186  OTHER  SPOROZOA 

ticks  (Dermacentor) ,  and  undoubtedly  will  be  found  in  other  ar- 
thropods. Their  occurrence  in  non-bloodsucking  insects,  aside 
from  the  fact  that  no  vertebrate  disease  is  known  to  be  associated 
with  many  of  these  infections  in  parasitic  insects,  is  evidence  for 
the  fact  that  these  organisms,  like  the  intestinal  flagellates  of 
insects  (see  p.  75),  are  primarily  parasites  of  arthropods,  a  com- 
paratively few  species  of  which  have  become  adapted  to  live  in 
the  blood  of  vertebrate  animals,  where  they  may  cause  disease. 

The  human  diseases  with  which  Rickettsia-like  bodies  have  been 
definitely  associated  are  typhus,  trench  fever,  and  Rocky  Mountain 
spotted  fever.  In  the  Japanese  disease,  kedani  or  tsutsugamushi, 
which  shows  some  affinities  with  spotted  fever,  parasites  have  been 
described  which  may  be  referable  to  this  group. 

Typhus  Fever.  —  This  deadly  disease,  which  so  frequently 
breaks  out  when  human  beings  are  crowded  together  where  per- 
sonal care  and  cleanliness  are  either  neglected  or  impossible, 
has  for  ages  been  associated  with  wars  and  prison  camps.  In 
some  parts  of  Europe  and  North  America  typhus  persists  in  an 
endemic  or  mild  epidemic  state,  ready  to  burst  into  flame  when 
opportunity  comes,  giving  rise  to  terrible  epidemics.  The  dis- 
ease is  endemic  on  the  Mexican  plateau,  where  it  is  known  as 
tabardillo. 

Typhus  has  a  sudden  onset,  and  is  characterized  by  high  fever, 
headache,  aches  in  the  bones  and  muscles,  bronchial  troubles, 
congestion  of  peripheral  blood-vessels  and  a  red  rash  later  giving 
rise  to  dark  blotches.  In  an  endemic  state  the  mortality  is  very 
low,  but  when  an  epidemic  breaks  out  there  may  be  50  to  79  per 
cent  mortality. 

Typhus  has  been  conclusively  shown  to  be  transmitted  prin- 
cipally, and  perhaps  solely,  by  body  lice.  Details  of  the  role  of 
the  lice,  and  an  account  of  some  recent  epidemics,  will  be  found 
on  pp.  397  to  399. 

Attention  was  first  directed  to  minute  granules  associated  with 
typhus  fever  by  Ricketts  in  1909,  but  these  bodies  were  first 
described  in  detail  from  typhus-infected  lice  by  Rocha-Lima  in 
1916  and  named  Rickettsia  prowazeki.  The  organism  occurs  in 
abundance  in  the  gut  of  infected  lice  as  single  granules,  diploid 
bodies,  or  in  clumps  evidently  resulting  from  continued  multi- 
plication without  separation  of  the  individuals;  occasionally 
bacillus-like   or   thread   forms   occur.     Multiplication   seems   to 


TRENCH   FEVER  187 

take  place  inside  the  epithelial  cells  of  the  insect.  This  organism 
has  been  found  in  the  blood  and  tissues  of  typhus  patients  also. 

A  great  deal  of  dispute  concerning  the  relationship  of  Rickett- 
sia prowazeki  to  typhus  has  arisen  from  the  fact  that  Rickettsia 
also  occurs  in  lice  which  could  not  have  been  infected  from  typhus 
patients.  It  is  now  generally  believed  that  there  is  a  distinct 
species  or  variety  of  Rickettsia,  named  R.  pediculi,  which  is  an 
inhabitant  of  the  gut  of  the  body  louse,  but  which  is  non-patho- 
genic to  man,  in  fact  probably  limited  to  the  insect  host. 

Trench  Fever.  —  This  disease,  which  was  unknown  before  the 
great  war,  but  which  was  one  of  the  most  important  diseases 
afflicting  troops  participating  in  it,  was  shown  in  1918  by  a  com- 
mission of  the  Medical  Research  Committee  of  the  American 
Red  Cross  and  also  by  a  British  committee  to  be  normally  trans- 
mitted by  body  lice  (see  p.  399),  although  the  possibility  of  trans- 
mission by  body  excretions  also  exists.  A  form  of  the  disease 
occurring  in  Central  Europe  was  known  as  Volhynian  fever. 

After  an  incubation  period  which  is  probably  usually  between 
14  and  30  days,  there  is  a  sudden  onset  of  fever  accompanied  by 
headache,  dizziness,  muscular  pains  and  other  symptoms.  The 
fever  may  last  continuously  for  several  weeks,  or  it  may  be  more 
or  less  definitely  relapsing.  In  most  cases  the  spleen  is  enlarged, 
and  there  is  a  rash  on  the  back,  chest  and  abdomen.  Usually 
the  patient  recovers  in  from  five  to  six  weeks,  but  the  illness  may 
be  greatly  prolonged. 

In  1916  Toepfer  first  described  a  species  of  Rickettsia,  R.  quin- 
tana,  as  occurring  in  lice  fed  on  trench  fever  patients.  This  or- 
ganism closely  resembles  that  of  typhus  fever  but  is  more  con- 
stantly rounded  or  diploid  in  form,  and  most  writers  agree  that  it 
does  not  occur  inside  the  epithelial  cells  of  the  gut  of  the  louse. 
This  parasite  may  be  merely  a  pathogenic  variety  of  R.  pediculi, 
mentioned  in  the  preceding  section,  which  has  acquired  the  ability 
to  thrive  in  human  blood.  In  infected  lice  the  organisms  are 
found  attached  to  the  surface  of  the  cells  of  the  midgut.  They 
gradually  fill  the  lumen,  and  are  eventually  voided  with  the  faeces. 

According  to  Hindle,  who  is  inclined  to  regard  the  organisms 
as  bacteria  rather  than  protozoa,  no  distinct  portion  of  the  life 
cycle  occurs  in  the  louse,  this  insect  merely  acting  as  a  culture 
tube  as  does  the  flea  for  the  bacilli  of  plague.  The  negative  period 
of  four  or  five  days  after  a  louse  becomes  infected  until  it  is  ca- 


188 


OTHER  SPOROZOA 


pable  of  transmitting  the  disease,  Hindle  thinks  is  probably  due  to 
insufficient  numbers  of  Rickettsia  in  the  Hce.  In  the  human  host 
the  parasites,  as  shown  by  transmission  experiments,  occur  in 
the  blood  plasma  and  also  in  various  body  excretions.  They  are 
ordinarily  not  filterable,  but  in  some  stages  of  their  development 
will  pass  through  bacterial  filters. 

Rocky   Mountain   Spotted   Fever.  —  For  many  years  certain 
limited  districts  in  the  Rocky  Mountain  region  of  northwestern 

United  States  (Fig.  57),  partic- 
ularly Idaho  and  Montana, 
have  been  known  to  be  affected 
by  this  very  serious  disease. 
Its  yearly  occurrence  in  well- 
defined  areas  has  given  rise  to 
panic  and  hysterical  fear  of  en- 
tering the  ''  haunted  "  places. 
Houses  were  deserted,  land  de- 
preciated in  value,  and  some  of 
the  richest  valleys  in  the  North- 
west left  unpopulated.  In  1906 
it  was  shown  by  Ricketts  that 
the  disease  was  invariably  pre- 
ceded by  the  bite  of  a  common 

Fig.  57.     Map  showing  distribution  of  local    WOOd-tick,     Dermaceutor 
Rocky    Mountain    spotted    fever.       Com-  ,         .  ^^^  i   t-c 

piled  from  U.  S.  Public  Health  Reports.        veuustus   (see  p.    361,   and  Fig. 

156),  which  was  experimentally 
shown  to  be  the  intermediate  host  of  the  parasite.  Wolbach  in 
1919  demonstrated  the  regular  appearance  of  minute  organisms, 
which  he  named  Dermacentroxenus  rickettsi,  in  the  cells  of  blood- 
vessels of  infected  mammals,  and  also  in  nearly  all  the  tissues  of 
infected  ticks.  The  organism  shows  several  morphological 
types,  but  most  frequently  appears  as  paired  lanceolate  bodies, 
the  length  of  a  pair  being  about  l/z.  It  is  transmitted  by  ticks 
to  their  young  with  the  eggs.  It  requires  from  two  to  ten  hours 
feeding  for  a  tick  to  become  infective,  but  after  an  incubation 
period  of  a  few  days  it  may  remain  infective  for  many  months. 
Although  D.  venustus  appears  to  be  the  only  transmitter  in  nature, 
experimentally  other  ticks  have  been  shown  to  act  as  suitable 
hosts. 

In  man  the  incubation  period  is  usually  from  four  to  seven 


ROCKY  MOUNTAIN  SPOTTED  FEVER  189 

days.  The  disease  begins  with  a  general  feehng  of  illness  fol- 
lowed by  chills  and  aches.  A  constant  fever  gradually  increases 
until  the  tenth  or  twelfth  day,  when  death  is  Ukely  to  occur. 
In  mild  cases  the  fever  gradually  subsides  during  the  five  or  six 
days  following.  Usually  on  the  third  day  a  rose-colored  rash 
breaks  out  on  the  head  and  upper  part  of  the  body,  followed  a 
day  or  two  later  by  a  characteristic  spotting  of  the  arms  and 
legs,  and  later  of  much  of  the  body,  caused  by  the  bursting  of 
blood  capillaries  in  the  skin.  The  spots  often  become  brownish 
or  grayish  in  color,  giving  the  spotted  appearance  from  which 
the  disease  takes  its  name.  In  Montana,  especially  in  the  Bitter 
Root  Valley,  the  disease  has  a  high  fatality,  75  per  cent  or  more 
of  the  cases  ending  in  death.  The  fatality  is  also  high  in  eastern 
Oregon,  but  in  other  endemic  regions  is  very  much  lower.  The 
disease  appears  only  in  spring  and  early  summer  when  ticks  are 
abundant.     So  far  no  specific  remedy  has  been  discovered. 

There  is  evidence  that  spotted  fever  may  be  harbored  by  some 
of  the  wild  mammals  on  which  the  wood  tick  normally  occurs, 
but  this  has  not  yet  been  proved.  The  transmitting  tick,  D. 
venitstus,  is  a  species  which  requires  two  years  to  reach  maturity. 
In  its  immature  stages  it  infests  many  of  the  local  rodents,  nearly 
all  of  which  are  susceptible  to  the  disease,  and  capable  of  trans- 
mitting it  to  uninfected  ticks.  As  adults  the  ticks  live  on  many 
of  the  larger  wild  animals  and  on  domestic  animals,  especially 
cattle  and  horses.  Whether  some  of  these  animals  may  be 
carriers  of  spotted  fever  has  not  been  determined. 

Prevention  of  spotted  fever  consists  primarily  in  fighting  ticks 
by  various  methods  (see  p.  368),  and  in  destroying  rodents,  both 
to  reduce  the  number  of  host  animals  for  the  young  ticks,  and  to 
prevent  the  possibility  of  their  acting  as  carriers  of  the  disease. 

There  is  grave  danger  that  spotted  fever  may  be  introduced 
into  other  parts  of  the  country  where  suitable  ticks  for  trans- 
mitting it  can  be  found.  The  exportation  by  railroad  of  wild 
deer,  elk,  goats  or  other  tick-infested  animals  to  zoological  parks 
or  government  preserves  is  a  dangerous  proceeding  unless  great 
care  is  taken  to  destroy  all  ticks  and  to  exclude  any  individuals 
which  might  be  harboring  the  disease  germ.  The  occasional 
occurrence  of  the  disease  in  various  parts  of  the  United  States 
should  be  carefully  watched  for,  and  every  precaution  taken  to 
prevent  local  ticks  from  getting  access  to  the  infection. 


190  OTHER  SPOROZOA 

Kedani  or  Japanese  Flood  Fever.  —  In  certain  parts  of  Japan 
there  occurs  a  disease  usually  called  kedani,  or  tsutsugamushi, 
which  is  reminiscent  of  American  spotted  fever.  It  begins  after 
an  incubation  of  five  or  six  days  or  longer  with  a  fever  and  break- 
ing out  of  the  skin,  the  fever  reaching  its  height  between  the 
third  and  seventh  days.  It  lasts  from  one  to  three  weeks  and 
is  accompanied  by  a  swelling  of  the  lymph  glands,  especially  in 
the  vicinity  of  the  point  of  infection.  This  is  usually  the  armpit, 
neck  or  groin  region,  where  a  small  ulcerous  wound  can  be  found 
resulting  from  the  bite  of  a  mite. 

The  disease  is  transmitted  by  the  bite  of  a  very  small  reddish 
mite,  probably  an  immature  mite  of  the  genus  Tromhidium, 
or  harvest  bug.  These  mites  live  in  great  numbers  on  a  very 
abundant  local  field-mouse,  Microtus  montehelli.  The  mice  are 
not  only  the  hosts  of  the  mites  but  are  also  subject  to  the  disease 
and  undoubtedly  are  an  important  factor  in  its  distribution  and 
control.  Kedani  is  apparently  most  common  in  laborers  working 
in  hemp  fields  in  July  and  August,  on  the  plains  which  are  an- 
nually flooded  by  the  overflow  of  certain  rivers. 

In  Sumatra  a  similar  disease,  which  is  either  identical  or  closely 
related  to  kedani,  occurs  commonly  among  Chinese  and  Japanese 
laborers  in  the  tobacco  fields.     The  disease  as  it  occurs  in  Su- 
matra,  where   it   is   called   pseudo-typhus, 
differs    in    some    slight   respects  from   the 
typical   Japanese  disease   and   has   a  very 
much    lower    fatality.      In    its    incubation 
period,  eruption,  and  general  course  it  re- 
sembles  spotted   fever   more    closely  than 
does  the  Japanese  disease,  and  Schueffner, 
who  has  worked  most   with    it,   thinks  it 
,  -^P-  „  ^?-     "  Granular  j^       |^g   transmitted    by    ticks  as  well  as 

bodies       m    mononuclear         *^  •  i  i        i 

leucocyte,  supposed  to  be  mites.     The  disease  has  also  been  reported 
parasites      of      Kedani  ^^^^  ^^iQ  Philippines,  and  about  150  cases 

{Theilena  tsutsugamushi).  ^^  .  tv/t   i          oi 

(After  Hayashi.)  have  been  reported  m   the   Malay  States. 

It  is  not  improbable  that  it  will  be  found 
to  be  widely  distributed  in  southeastern  Asia,  having  been  in- 
correctly diagnosed  as  other  diseases. 

A  number  of  organisms  thought  to  be  the  cause  of  Kedani  have 
been  described.  Hayashi  has  recently  found  granular  bodies  of 
several  morphological  types  in  both  the  plasma  and  cells  of  the 


CHLAMYDOZOA 


191 


blood  of  infected  individuals,  and  in  the  primary  sore.  These 
he  believed  to  be  piroplasma-like  organisms,  and  named  them 
Theileria  tsutsugamushi.  From  the  description  and  figures  of 
these  organisms,  however,  it  seems  more  probable  that  they  are 
related  to  Rickettsia  or  Dermacentroxenus.  The  blood  of  infected 
individuals  injected  subcutaneously  causes  the  disease.  The 
organisms  do  not  pass  through  bacterial  filters. 

Prevention  in  the  endemic  regions  obviously  consists  in  avoid- 
ing mites  by  skin  applications  or  other  means.  The  extinction 
of  the  field-mice  and  with  them  most  of  the  mites  would  un- 
doubtedly lessen  the  danger  of  the  disease. 

Chlamydozoa 

The  protozoan  affinities  claimed  for  the  parasites  or  parasite- 
like bodies  included  in  the  so-called  Chlamydozoa  is,  as  said 
before,  doubtful,  and  new  investigations  do  not,  in  most  cases, 
tend  to  substantiate  the  claim  of  these  structures  to  considera- 
tion as  animal  parasites.  A  brief  account  of  the  parasites  or  cell 
inclusions  in  some  of  the  principal  diseases  attributed  to  this  group 
is  all  that  can  be  given  here. 

Smallpox  and  Vaccine.  —  The  youngest  forms  of  the  parasite 
are  minute  granules  or  "  elementary  bodies  "  measuring  about 
0-5  M  (50:000  oi  an  inch)  in  diameter.  As  growth  takes  place 
the  granules  increase  in  number  and  become  surrounded  by 
material  which  is  usually  interpreted  as  a  reaction  product  of 
the  cell,  forming  the  "  Guarnieri  bodies  "  (Fig.  59 A).  These 
eventually  rupture,  liberating  the  granules  to  infect  new  cells. 
The  smallpox  parasites  differ  from  those  of  cowpox  in  that  they 
attack  the  nuclei  as  well  as  the  cytoplasm  of  the  cells. 

Scarlet  Fever.  —  In  the  skin  cells  of  scarlet-fever  patients  are 
found  characteristic  inclusions  which  have  been  referred  to  the 
Chlamydozoa  and  named  Cyclasterion  scarlatince  (Fig.  59B). 
These  bodies  in  one  stage  of  their  development  are  of  irregular 
shape  with  numerous  enclosed  granules,  while  in  another  stage 
the  granules  become  radiately  arranged  around  a  larger  central 
body. 

Hydrophobia  or  Rabies.  —  There  usually  occur  in  certain  brain 
cells  of  animals  suffering  from  hydrophobia  specific  bodies  which 
are  popularly  known  as  "  Negri  bodies  "  in  honor  of  their  discov- 
erer, and  which  have  been  given  the  scientific  name  Neurorydes 


192 


CHLAMYDOZOA 


VACCINE 

Cornea  cells  showing  developmental  stages  of  Guarnieri  bodies,  Cytoryctes  vac- 
cinice.     (After  Tyzzer.) 


B 


SCARLET  FEVER 

Epithelial  cells  of  skin  showing  various  stages  in  development  of  Mallory  bodies, 
Cyclasterion  scarlatinoe.    Radiate  form  shown  in  middle  figure.     (After  Mallory.) 


-•Rb. 


TRACHOMA 

Epithelial  cell  of  conjunctiva  showing  Prowazek  bodies.     (After  Halberstaedter.) 


RABIES    OR    HYDROPHOBIA 


Nerve  cells  of  Ammon's  horn  of  cerebrum  showing  Negri  bodies,  Neuroryctes 
hydrophobioB.     (After  Maresch.) 


Fig.  59.  — Various  types  of  Chlamydozoa.  Note  that  in  each  case  the  parasite- 
like bodies  are  enclosed  in  a  ground  substance  supposed  to  be  extruded  by  the 
nucleus. 


CHLAMYDOZOA  193 

hydrophohice  (Fig.  59D).  At  first  thought  to  be  simple  parasites, 
these  bodies  are  now  generally  regarded,  as  are  other  Chlamydozoa, 
as  reaction  products  of  the  host  cell  surrounding  one  or  many  mi- 
nute granules  which  are  the  true  parasites.  The  minute  size  of 
the  granules  and  the  difficulty  of  identifying  them  when  they  are 
separated  from  their  "  mantles "  probably  accounts  for  the 
negative  findings  in  infective  parts  of  the  nervous  system  in 
which  Negri  bodies  are  not  found,  and  also  in  the  saliva,  which  is 
highly  infective.  The  weight  of  evidence  seems  to  favor  the 
protozoan  affinities  of  the  microorganism  of  hydrophobia,  but 
the  nature  of  the  parasite  is  still  shrouded  in  uncertainty. 

Trachoma.  —  The  belief  in  the  protozoan  nature  of  the  parasite 
of  trachoma,  a  disease  of  the  eyes  causing  inflammation  of  the  con- 
junctiva, rests  on  similar  ground.  In  the  affected  portions  of  the 
eye  are  found  numerous  tiny  granules  known  as  ^'  Prowazek's 
bodies  "  (Fig.  59C),  sometimes  within  the  cells  and  even  within  the 
nuclei  and  #  at  other  times  free  in  the  serum,  which  have  been 
thought  to  be  the  cause  of  the  disease.  The  fact  that  these  bodies 
are  sometimes  found  in  other  affections  has  thrown  some  doubt 
on  their  relation  to  trachoma.  Recent  investigations  by  Anna 
Williams  of  4000  school  children  in  New  York  with  eye  infec- 
tions or  inflammations,  none  of  which  were  typical  cases  of  '*  tra- 
choma," showed  "  trachoma  inclusions  "  to  be  common,  and  gave 
evidence  that  these  inclusions  were  in  reality  "  nests  "  of  growing 
bacteria,  of  various  kinds,  in  the  epithelial  cells  of  the  conjunc- 
tiva. Miss  Williams'  investigations  throw  doubt  on  the  existence 
of  a  specific  disease  to  which  the  name  trachoma  can  be  applied. 

Other  Diseases  Caused  by  Obscure  Parasites 

The  diseases  mentioned  above  are  those  which  are  most  com- 
monly thought  .to  be  caused  by  organisms  of  this  problematic 
group,  Chlamydozoa.  There  are  a  number  of  others,  however, 
which  may  belong  here,  but  on  which  much  further  investigation 
is  necessary.  Among. these  are  foot-and-mouth  disease,  in  which 
Stauffacher  has  recently  found  an  organism,  Aphthomonas  infes- 
tans,  which,  however,  is  probably  more  closely  related  to  Leish- 
mania  (see  p.  76);  verruga  peruviana,  which  in  some  respects 
resembles  smallpox;  the  ubiquitous  measles;  and  a  number  of 
diseases  which  are  of  rare  or  of  more  or  less  limited  distribution. 
That  all  of  these  diseases,  or  even  all  of  those  separately  discussed 


194  OTHER  SPOROZOA 

above,  are  caused  by  protozoan  parasites  is  very  doubtful,  and 
only  further  investigation  can  determine  the  true  status  of  their 
causative  microorganisms.  The  recent  development  of  knowledge 
concerning  such  groups  of  pathogenic  organisms  as  the  Spiro- 
chaetes  and  Rickettsia-like  organisms,  on  the  border  line  of  visibil- 
ity, leads  to  speculation  as  to  whether  some  of  these  other  diseases 
may  not  be  found  to  be  caused  by  parasites  of  similar  nature. 


PART  II  — WORMS 

CHAPTER  XI 
INTRODUCTION   TO   THE   "WORMS" 

Classification.  —  The  name  worm  is  an  indefinite  though  sug- 
gestive term  which  is  popularly  applied  to  any  elongated  creeping 
thing  which  is  not  obviously  something  else.  There  is  hardly 
a  branch  or  phylum  of  the  Animal  Kingdom  which  does  not 
contain  members  to  which  the  term  "  worm  "  has  been  applied, 
not  excepting  the  great  group  Chordata,  to  which  the  back- 
boned animals,  including  man  himself,  belong.  In  fact  some 
animals,  such  as  many  insects,  are  "  worms  "  during  one  phase 
of  their  life  history,  and  something  quite  different  during  another. 

In  a  more  restricted  sense  the  name  "  worm  "  is  applied  to  three 
great  groups  of  animals,  with  a  few  outlying  forms,  which  super- 
ficially all  resemble  one  another  in  being  unquestionably  "  worm- 
like," though  in  life  and  structure  they  are  widely  different. 
To  these  animals,  together  with  a  few  other  heterogeneous  forms, 
the  collective  name  "  Vermes,"  meaning  worms,  was  applied  by 
the  early  workers  on  zoological  classification.  Upon  more  de- 
tailed study  it  became  obvious  that  different  types  of  the  ''  Ver- 
mes "  differed  from  one  another  to  such  an  extent  that  they 
would  have  to  be  divided  into  several  great  branches  or  phyla  of 
the  Animal  Kingdom.  At  the  present  time  the  majority  of  these 
animals  are  classified  in  three  phyla,  as  follows:  the  Platyhel- 
minthes  or  flatworms,  the  Nemathelminthes  or  roundworms 
and  the  Annelida  or  segmented  worms.  There  are  a  number  of 
"  worms  "  which  will  not  readily  fit  into  any  of  these  groups  but 
are  incertoe  sedis,  showing  affinity  to  one  group  in  some  respects 
and  to  another  in  others.  Some  species  are  so  profoundly  modi- 
fied by  their  peculiar  modes  of  life  that  it  is  practically  impossible 
even  to  guess  at  their  true  relationships.  All  three  of  the  phyla 
of  '*  worms  "  contain  parasitic  species,  though  none  of  them  con- 
tain parasites  exclusively. 

Flatworms.  —  The  group  of  lowest  organization  is  the  Platyhel- 
minthes.     The  worms   included   in   this   phylum   are   flattened 

196 


FLATWORMS 


197 


from  the  dorsal  to  the  ventral  side,  whence  the  common  name 
"  flat  worms."  Unlike  nearly  all  other  many-celled  animals 
they  have  no  body  cavity,  the  organs  being  embedded  in  a  sort 
of  spongy  "  packing  "  tissue.  The  digestive  tract  has  only  a 
single  opening  which  serves  both  for  mouth  and  vent  (Fig.  60A), 
and  in  the  tapeworms  the  entire  alimentary  canal  is  absent. 
The  nervous  system  is  very  simple.  Performing  the  function 
of  kidneys  is  a  system  of  tubes,  the  terminal  branches  of  which 
are  closed  by  ''  flame  cells,"  so  called  from  the  flamelike  flickering 
of  a  brush  of  cilia  which  keeps  up  a  flow  of  fluid  toward  the 


Fig.  60.  Types  of  digestive  tracts  in  worms;  A,  fluke,  —  note  branching  and 
absence  of  anus;  B,  roundworm,  —  note  simple  form,  with  only  pharynx  differen- 
tiated, and  presence  of  anus;  C,  leech,  —  note  extensive  pouches  or  ccEca  which 
serve  as  reservoirs  for  surplus  food. 


larger  branches  of  the  system  and  ultimately  to  the  excretory 
pore,  thus  conducting  the  waste  products  out  of  the  body.  The 
absence  of  any  kind  of  blood  system  or  other  apparatus  for  trans- 
porting food  or  waste  products  in  the  body  necessitates  a  branched 
condition  of  the  digestive  and  excretory  systems.  The  most 
highly  developed  system  of  organs  and  one  which  occupies  a 
large  portion  of  the  body  is  that  concerned  with  reproduction. 
Usually  there  is  a  complete  male  and  female  system  in  each 
worm  and  in  some  tapeworms  there  is  a  double  system  of  each 
kind. 

The  flatworms  are  usually  divided  into  three  classes,  the  Tur- 
bellaria,  the  Trematoda  and  the  Cestoda.  The  Turbellaria  are 
for  the  most  part  free-living  animals  and  include  the  "  pla- 
narians  "  which  can  be  found  creeping  on  the  under  side  of  stones 
in  ponds.  The  Trematoda  include  the  flukes,  all  of  which  are 
parasitic,  some  externally  on  aquatic  animals,  others  internally 


198  INTRODUCTION  TO  THE  WORMS 

on  aquatic  or  land  animals.  They  are  flattened  animals,  usually 
oval  or  leaf-shaped,  furnished  with  suckers  for  adhering  to  their 
hosts.  The  flukes  which  live  as  external  parasites  of  aquatic 
animals  have  a  comparatively  simple  life  history,  while  those 
which  are  internal  parasites  of  land  animals  have  a  complex 
life  history,  in  the  course  of  which  they  pass  through  two  or  three 
different  hosts.  The  third  class,  Cestoda,  is  comprised  by  the 
tapeworms.  As  adults  they  are  all  parasites  of  the  digestive  tracts 
of  various  animals  and  are  profoundly  modified  for  this  kind 
of  an  existence.  Their  peculiar  method  of  multiplication  by  bud- 
ding results  in  the  formation  of  a  chain  of  segments,  sometimes 
of  great  length,  which  collectively  constitute  a  tapeworm;  each 
segment,  however,  is  practically  complete  in  itself  and  capable  of 
separate  existence  if  it  had  some  method  of  retaining  its  position 
in  the  host's  intestine.  Some  tapeworms  have  a  life  history 
comparable  in  its  complexity  with  that  of  the  flukes  but  as  a 
rule  it  is  much  simpler.  With  the  flatworms  are  usually  asso- 
ciated the  Nemertinea,  marine  worms  some  of  which  are  more 
or  less  parasitic.  None  of  them  is  of  any  interest  in  connection 
with  human  parasitology. 

Roundworms.  —  Of  somewhat  higher  organization  than  the 
flatworms  is  the  phylum  Nemathelminthes  or  roundworms. 
These  worms  are  cylindrical  instead  of  flattened,  they  possess  a 
body  cavity,  and  they  have  an  opening  at  each  end  of  the  digestive 
tract  (Fig.  GOB).  The  excretory  system  usually  consists  of  simple 
tubes  running  the  length  of  the  body.  The  presence  of  a  fluid- 
filled  body  cavity  through  which  food  and  other  substances  can 
diffuse  obviates  the  necessity  for  having  branched  organs.  The 
sexes  are  separate,  and  the  reproductive  systems  are  much 
simpler  than  in  the  flatworms. 

Usually  there  is  only  a  single  class  recognized  as  belonging  to 
this  phylum,  namely,  the  Nematoda  or  nematodes.  Some  of 
the  nematodes  are  not  parasitic  but  many  of  them  parasitize 
either  plants  or  animals.  There  are  many  important  human 
parasites  among  the  Nematoda,  for  instance,  the  hookworms, 
pin  worms,  Ascaris  and  other  intestinal  worms,  Trichinella,  Filaria 
and  the  guinea-worm.  In  some  of  these  the  life  history  is  fairly 
simple  while  in  others  it  is  more  complex  and  involves  two  dif- 
ferent hosts. 

Some  zoologists  associate  with  this  phylum  two  other  classes 


ANNELIDS  199 

of  worms,  the  Acanthocephala  and  the  Nematomorpha.  The 
former  class,  as  indicated  by  the  name,  include  the  spiny-headed 
worms.  These  are  cylindrical  worms  of  peculiar  anatomy, 
notable  for  the  complete  absence  of  a  digestive  tract  as  in  the 
tapeworms.  The  head  is  furnished  with  a  proboscis  which  is 
armed  with  rows  of  thornlike  booklets.  The  adults  live  in  the 
digestive  tracts  of  their  hosts,  burying  the  thorny  proboscis 
deep  into  the  mucous  membranes.  They  have  a  complex  Hfe 
history,  the  larval  stage  being  passed  in  insects  of  various  kinds. 
Several  species  are  occasionally  but  rarely  found  in  man. 

The  class  Nematomorpha  is  comprised  by  the  "  horse-hair 
snakes,"  so  called  from  the  popular  belief  that  they  develop  from 
horse  hairs  which  fall  into  water.  They  are  exceedingly  long 
slender  worms,  usually  parasitic  in  insects.  Occasionally  they 
are  accidentally  swallowed  by  man  with  drinking  water  and  are 
usually  vomited,  much  to  the  surprise  and  horror  of  the  tempo- 
rarily infected  person. 

Annelids.  —  The  most  highly  organized  phylum  of  worms  is 
Annelida,  including  the  segmented  worms  or  annelids.  In  three 
important  respects  these  worms  are  the  first  animals  in  the  scale 
of  evolution  to  develop  the  type  of  structure  characteristic  of 
the  vertebrate  animals,  consisting,  namely,  in  a  division  of  the 
body  into  segments,  in  the  presence  of  a  blood  system,  and  in 
the  presence  of  "  nephridia  "  or  primitive  excretory  organs  of 
the  same  fundamental  type  as  are  the  kidneys  of  higher  animals. 
In  addition  the  digestive  system  is  highly  developed  and  there  is 
a  well-developed  nervous  system  distinctly  concentrated  in  the 
head.  In  some  annelids  the  sexes  are  separate,  while  in  others 
both  reproductive  systems  occur  in  the  same  individual. 

At  least  three  classes  of  Annelida  are  usually  recognized,  namely 
the  Archi-annelida,  including  a  few  primitive  marine  forms; 
the  Chsetopoda,  including  the  worms  which  are  furnished  with 
bristles  or  setse,  such  as  the  earthworms  and  marine  sand  worms; 
and  the  Hirudinea  or  leeches,  in  which  there  are  two  suckers  but 
no  setse.  There  are  a  number  of  other  groups  of  worms  which 
many  zoologists  include  with  the  annelids,  but  as  their  systematic 
position  is  doubtful  and  as  they  include  no  parasitic  forms  they 
need  not  be  mentioned  here.  The  only  class  of  annelids  which 
includes  parasites  of  man  are  the  Hirudinea  or  leeches.  These 
animals  superficially  resemble  flatworms  but  they  can  readily 


200  INTRODUCTION  TO  THE  WORMS 

be  recognized  externally  by  the  segmentation  of  the  body; 
the  internal  anatomy  is  totally  different.  Both  sexes  are  repre- 
sented in  each  individual. 

The  number  of  different  species  of  worms  in  these  three  phyla 
which  have  been  found  in  man  is  well  up  in  the  hundreds.  In 
the  following  pages  each  group  of  these  worms  which  contains 
important  human  parasites  will  be  dealt  with,  but  only  those 
species  which  are  important,  or  which  are  particularly  inter- 
esting from  some  other  point  of  view,  will  be  individually 
considered. 

Parasitic  Habitats.  —  As  to  the  parts  of  the  body  which  may 
be  attacked  by  worms  of  one  kind  or  another,  there  is  hardly 
any  organ  or  tissue  which  is  exempt.  There  are  flukes  which 
habitually  infest  the  intestine,  liver,  lungs  and  bloodvessels, 
and  one  species  occasionally  wanders  to  the  muscles,  spleen, 
brain  and  many  other  organs.  The  adult  tapeworms  are  all 
resident  in  the  small  intestine,  but  larval  tapeworms  are  found 
in  various  locations  in  the  body.  The  majority  of  the  parasitic 
nematodes  of  man  are  found  in  the  intestinal  canal  but  there 
are  exceptions  to  this.  The  adult  TrichinelloB,  for  instance, 
inhabit  the  intestine,  but  the  larvae  are  found  in  the  muscles; 
the  adult  Filarice  usually  live  in  the  lymph  vessels,  whereas  the 
larvae  swarm  in  the  blood;  the  guinea- worm  and  some  other 
nematodes  creep  under  the  skin  in  the  connective  tissue;  the 
lungworm  of  the  hog,  Metastrongylus  apri,  which  occasionally 
occurs  in  man,  infests  the  lungs  and  bronchial  tubes;  and  Dioc- 
tophyme  renale  (or  Eustrongylus  gigas)  is  an  occasional  human 
parasite  which  occurs  in  the  kidneys  and  rarely  in  the  body  cavity. 
The  leeches,  on  the  other  hand,  are  parasitic  on  the  surface  of 
the  body  or  in  the  cavities  of  the  nose  and  mouth. 

Life  History  and  Modes  of  Infection.  —  The  life  history  and 
mode  of  infection  of  worms  varies  with  the  habitat  in  the  body. 
Every  parasitic  worm  must  have  some  method  of  gaining  access 
to  the  body  of  its  host,  and  must  have  some  means  for  the  escape 
of  its  offspring,  either  eggs  or  larvae,  from  the  host's  body  in 
order  to  continue  the  existence  of  its  race.  Many  species  utilize 
intermediate  hosts  as  a  means  of  transfer  from  one  host  to  an- 
other; others  have  a  direct  life  history,  i.e.,  they  either  develop 
inside  the  escaped  egg  and  depend  on  such  agencies  as  food  and 
water  to  be  transferred  to  a  new  host,  e.g.,  pinworm,  or  they 


EFFECTS  OF  PARASITISM  201 

develop  into  free-living  larvae  which  are  swallowed  by  or  burrow 
into  a  new  host  when  opportunity  offers,  e.g.,  the  hookworms. 

Most  of  the  intestinal  parasites  apparently  enter  their  host 
by  way  of  the  mouth,  and  the  eggs  escape  with  the  faeces.  Many 
species  enter  as  larvae  in  the  tissues  of  an  intermediate  host  which 
is  eaten  by  the  final  host.  Of  such  a  nature  are  most  of  the 
tapeworms  and  flukes  and  some  nematodes,  e.g.,  Trichinella. 
Some  nematodes  of  the  intestine,  as  the  pinworm  and  whip- 
worm, enter  contaminated  food  or  water  as  fully  developed 
embryos  in  the  eggs.  Still  other  species,  as  the  hookworms  and 
Strongyloides,  usually  reach  their  destination  in  an  indirect  way 
by  burrowing  through  the  skin.  All  the  intestinal  worms  except 
Trichinella  produce  eggs  or  larvae  which  escape  from  the  body 
with  the  faeces.  In  Trichinella  the  larvae  encyst  in  the  muscles 
and  in  order  for  them  to  be  released  the  host  must  be  eaten  by 
another  animal.  Many  of  the  worm  parasites  of  other  organs 
of  the  body  also  enter  by  way  of  the  mouth  and  digestive  tract, 
though  they  have  various  means  of  exit  for  the  eggs  or  larvae. 
The  liver  flukes  enter  and  escape  from  the  body  as  do  ordinary 
intestinal  parasites;  the  lung  flukes  enter  by  the  mouth,  but  the 
eggs  are  expelled  with  sputum;  the  blood  flukes  enter  by  bur- 
rowing through  the  skin,  and  the  eggs  escape  either  with  faeces  or 
urine;  the  FilarioB,  like  blood-dwelling  protozoans,  enter  and 
leave  the  body  by  the  aid  of  blood-sucking  insects;  the  guinea- 
worm  enters  by  the  mouth,  and  the  larvae  leave  through  the  skin. 
The  larval  tapeworms  which  infest  man  enter  either  by  the 
mouth  or  by  accidental  invasion  of  the  stomach  from  an  adult 
in  the  intestine.  Like  Trichinella  they  are  usually  permanently 
sidetracked  in  man,  since  they  can  escape  only  by  being  eaten 
with  the  tissues  in  which  they  are  imbedded. 

Effects  of  Parasitism.  —  The  effects  produced  by  parasitic 
worms  depend  in  part  on  the  organs  or  tissues  occupied,  in  part 
on  the  habits  of  the  worms  and  in  part  on  the  poisonous  qualities 
of  their  secretions  or  excretions,  to  which  the  susceptibility  of 
different  individuals  is  very  variable.  The  effects  of  some  kinds 
of  worms  is  a  much  disputed  point.  Some  investigators  tend  to 
minimize  the  damage  done  by  worm  parasites,  especially  intestinal 
ones,  while  others  undoubtedly  overestimate  it.  Improved  facili- 
ties for  discovering  infection  have  demonstrated  the  presence  of 
intestinal  parasites  in  so  many  unsuspected  cases  that  we  are 


202  INTRODUCTION  TO  THE  WORMS 

likely  to  incriminate  them  in  nearly  every  morbid  condition  for 
which  we  cannot,  with  equal  readiness,  discover  another  cause. 
It  cannot  be  doubted,  however,  that  many  of  the  morbid  con- 
ditions really  are,  in  part  at  least,  produced  by  intestinal  worms. 
Much  of  the  difference  of  opinion  regarding  the  effects  of  these 
parasites  is  no  doubt  due  to  the  variable  susceptibility  of  dif- 
ferent individuals. 

The  amount  of  nutriment  which  is  absorbed  by  worms  such 
as  Ascaris  and  the  pin  worm,  which  live  on  semi-digested  food  in 
the  lumen  of  the  intestine,  is  probably  in  most  cases  relatively 
slight:  Leuckart  states  that  Tcenia  saginata,  for  instance,  gives 
off  about  11  proglottids  a  day,  which  would  amount  to  one  and 
two-thirds  pounds  in  a  year.  This  would  not,  of  course,  repre- 
sent more  than  a  fraction  of  the  food  materials  used.  Such  a 
loss  would,  however,  be  inappreciable  in  adults,  though  it  would 
be  felt  in  growing  children  unless  compensated  for  by  increased 
appetite.  Many  intestinal  parasites,  as  the  hookworms,  devour 
cells  of  the  mucous  membrane  and  suck  blood,  sometimes  causing 
extensive  bleeding. 

The  most  serious  injury  from  intestinal  worms  is  undoubtedly 
the  toxic  effects  of  their  secretions  and  excretions.  We  know 
that  the  diseases  caused  by  most  Bacteria  and  Protozoa  are 
the  result,  not  of  the  actual  damage  done  by  the  parasites  in 
devouring  tissues,  but  of  the  poisonous  waste  products  and  se- 
cretions given  off  by  these  organisms.  Until  recently  little  was 
known  about  the  toxic  effects  of  worms,  but  that  toxins  were  pro- 
duced by  them  was  evident  from  symptoms  disproportionate  to 
the  mechanical  injury  the  parasites  could  do,  and  from  effects 
which  could  in  no  way  be  the  direct  result  of  mechanical  injury. 
In  1901  a  French  worker,  Vaullegeard,  actually  obtained  from 
certain  tapeworms  and  from  Ascaris  toxic  substances  which 
acted  upon  the  nervous  system  and  upon  the  muscles.  Recent 
investigations  by  Flury  have  shown  that  Ascaris,  a  nematode, 
contains  certain  substances  which  are  very  irritating  to  mucous 
membranes,  other  substances  which  have  blood-destroying  and 
tissue-destroying  properties,  and  still  others  which  have  an  in- 
toxicating effect  on  the  nervous  system,  causing  hallucinations, 
dehrium  and  other  disturbances.  These  toxins,  derived  from 
the  body  and  excretions  of  Ascaris,  when  introduced  into  a  ver- 
tebrate animal,  cause  the  same  symptoms  which  often  accom- 


TOXIC  EFFECTS  203 

pany  Ascaris  infection,  but  which  have  usually  been  attributed 
to  other  causes.  With  such  an  array  of  formidable  chemical 
compounds  in  the  body  substance  of  intestinal  worms,  it  is  not 
necessary  to  search  for  mechanical  factors  to  explain  intestinal 
disturbances,  abdominal  pains,  nervous  and  mental  symptoms, 
and  the  various  other  apparently  unrelated  conditions  which 
accompany  infection  with  such  worms.  When,  as  in  the  case 
of  hookworms,  such  effects  are  combined  with  blood-sucking  and 
bleeding  from  wounds,  facilitated  by  secretions  which  prevent 
coagulation  of  blood,  it  is  not  difficult  to  understand  how  such 
profound  anemia  and  loss  of  vitality  are  produced  by  compara- 
tively few  small  worms.  The  presence  in  blood  of  toxins  ab- 
sorbed from  worms  in  the  intestine  is  further  indicated  by  changes 
in  the  blood  itself.  The  anemia  of  hookworm  disease,  due  both 
to  reduction  of  blood  corpuscles  and  to  diminution  in  percentage 
of  haemoglobin,  is  so  well  known  that  anemia  is  sometimes  used 
as  a  synonym  for  hookworm  disease.  Similar  though  usually 
less  marked  anemia  occurs  in  cases  of  infection  with  other  worms, 
e.g.,  the  fish  tapeworm,  Dihothriocephalus  latus,  the  blood  flukes, 
etc.  Another  symptom  of  the  presence  of  worms  in  the  body  is 
a  change  in  number  and  kinds  of  leucocytes  or  white  blood 
corpuscles.  An  almost  universal  symptom,  though  one  which  is 
occasionally  absent  even  in  the  infections  in  which  it  is  most 
characteristic,  is  an  increase  in  the  number  of  so-called  "  eosin- 
ophiles,"  white  blood  corpuscles  containing  granules  which 
stain  red  with  eosin.  These  cells  are  supposed  to  be  for  the  pur- 
pose of  destroying  toxins  in  the  blood  just  as  some  of  the  leuco- 
cytes are  apparently  for  the  purpose  of  capturing  and  destroying 
bacteria  or  other  foreign  cells.  The  mere  presence  of  an  in- 
creased number  of  them  is,  therefore,  sufficient  reason  for  as- 
suming the  presence  of  toxins  for  them  to  destroy.  The  normal 
number  of  eosinophiles  varies  from  one  per  cent  to  four  per  cent  of 
the  total  number  of  leucocytes,  whereas  in  infections  with  such 
parasites  as  trichina,  blood  flukes,  echinococcus  cysts,  etc., 
the  number  nearly  always  rises  to  five  per  cent  or  higher,  and  in 
some  cases  reaches  over  75  per  cent. 

Another  factor  which  is  undoubtedly  of  prime  importance  is 
the  portal  of  entry  which  intestinal  worms  give  to  Bacteria  and 
Protozoa.  We  have  awakened  to  the  importance  of  a  "  whole 
skin  "  and  the  danger  which  accompanies  the  piercing  of  it  by  the 


204  INTRODUCTION  TO  THE  WORMS 

unclean  probosces  of  biting  flies,  bugs  or  other  insects.  We  have 
not  yet  fully  awakened  to  the  importance  of  an  uninjured  mu- 
cous membrane.  As  has  been  pointed  out  by  Shipley,  the  in- 
testinal worms  play  a  part  within  our  bodies  similar  to  that 
played  by  blood-sucking  arthropods  on  our  skins,  except  that  they 
are  more  dangerous  since,  after  all,  only  a  relatively  small  per 
cent  of  biting  insects  have  their  probosces  soiled  by  organisms 
pathogenic  to  man,  whereas  the  intestinal  worms  are  constantly 
accompanied  by  bacteria,  such  as  Bacillus  coli,  which  are  capable 
of  becoming  pathogenic  if  they  gain  access  to  the  deeper  tissues 
as  they  are  able  to  do  through  the  injuries  made  by  hookworms, 
whipworms,  tapeworms,  etc.  Weinberg,  for  instance,  found  that 
whereas  he  was  unable  to  infect  unparasitized  apes  with  typhoid 
bacilli,  apes  infested  with  tapeworms  or  whipworms  readily  con- 
tracted typhoid  fever,  the  bacteria  presumably  gaining  entrance 
through  wounds  in  the  mucous  membrane  made  by  the  worms. 
The  relation  of  intestinal  worms  to  appendicitis  is  more  than 
hypothetical,  and  it  is  probable  that  far  more  cases  of  appendi- 
citis are  the  outcome  of  injury  done  by  worms  than  is  usually 
supposed.  Although  it  has  been  objected  that  very  few  of  the 
thousands  of  appendices  removed  yearly  are  reported  to  contain 
parasites,  it  must  be  pointed  out  that  parasites  are  very  seldom 
sought,  could  easily  be  overlooked,  and  might  not  be  recognized 
as  such  if  found.  It  is  furthermore  possible  that  parasites  which 
initiated  the  inflammation  and  ulceration  might  no  longer  be 
present  in  the  appendix  upon  its  removal,  since  they  are  able  to 
move  about  freely  in  the  digestive  tract.  Shipley  remarks  that 
appendicitis  is  a  commoner  disease  now  than  it  was  when  ver- 
mifuges were  more  frequently  given. 

Diagnosis.  —  The  diagnosis  of  infection  with  various  species  of 
worms  depends  principally  on  the  identification  of  their  eggs  or 
larvse  as  found  in  the  fseces  or  other  excretions  by  microscopic  ex- 
amination. Nearly  every  species  of  parasite  has  recognizably  dis- 
tinct characterics  of  the  eggs,  the  chief  variations  being  in  size, 
shape,  color,  thickness  of  shell,  stage  in  development,  appearance 
of  the  embryo  if  present,  and  presence  or  absence  of  an  operculum 
or  lid.  Some  of  the  commoner  worm  eggs  are  shown  in  a  com- 
parative way  in  Fig.  61. 


EGGS  OF  PARASITIC  WORMS 


205 


iL^i:j2^ 


Fig.  61. 


Eggs  of  parasitic  worms,  drawn  to  scale, 
authors.) 


X  200.     (After  various 


A,  Schistosoma     hoematobium,     voided      with  0, 

urine. 

B,  Schistosoma  mansoni,  voided  with  faeces.  P, 

C,  Schistosoma  japonicum,  voided  with  fseces. 

D,  Paragonimus  ringeri,  voided  with  sputum.  Q, 

E,  Fasciola  hepatica,  voided  with  fseces.  R, 

F,  Clonorchis  sinensis,  voided  with  faeces.  S, 

G,  Opisthorchis  felineus,  voided  with  faeces. 

H,    Opisthorchis  noverca,  voided  with  fseces.  T, 
I,     Fasciolopsis  buski,  voided  with  fseces. 

J,     Gastrodiscoides  hominis,  voided  with  faeces.  U, 

K,    Heterophyes  heterophyes,  voided  with  fseces.  V, 

L,     Yokagawa  yokagawa,  voided  with  faeces.  W, 

M,   Taenia  saginata,  voided  with  faeces,  usually  X, 

in  proglottids.  Y, 
N,    Tcenia  solium,  voided  with   faeces,  usually 

in  proglottids.  Z, 


Hymenolepis    nana,    voided    with     faeces, 

usually  in  proglottids. 
Hymenolepis  diminuta,  voided  with  faeces, 

usually  in  proglottids. 
Dibothriocephalus  latus,  voided  with  faeces. 
Diplogonoporus  grandis,  voided  with  faeces. 
Davainea    madagascariensis,     voided    with 

faeces,  usually  in  proglottids. 
Dipylidium   caninum,    voided    with    fseces, 

usually  in  proglottids. 
Ascaris  lumbricoides,  voided  with  faeces. 
Trichuris  trichiura,  voided  with  faeces. 
Ancylostoma  duodenale,  voided  with  faeces. 
Necalor  am,ericanus,  voided  with  faeces. 
Trichostrongylus     orientalis,     voided     with 

faeces. 
Oxyuris  vermicularis,  voided  with  faeces. 


206  INTRODUCTION   TO  THE  WORMS 

In  cases  of  heavy  infection  it  is  usually  possible  to  find  the  eggs 
in  the  faeces  or  other  excretions  by  simple  microscopic  exam- 
ination of  a  smear  made  directly  from  the  faecal  sample.  Many 
light  infections,  however,  escape  detection  by  this  method,  and 
various  means  of  concentrating  the  eggs  so  that  they  can  be  more 
readily  found  have  been  devised.  One  method  of  concentration 
is  to  mix  with  water,  strain,  and  centrifuge,  thus  eliminating 
coarse  material  and  throwing  the  relatively  heavy  eggs  to  the 
bottom  of  a  tube.  The  principal  objection  to  both  methods  is 
the  small  size  of  the  sample  which  is  examined. 

Several  methods  for  the  quick  and  efficient  examination  of 
large  samples  of  faeces  have  recently  been  devised.  One  method, 
known  as  the  glycerine-salt  method,  developed  by  Barber,  con- 
sists in  thoroughly  mixing  a  fairly  large  faecal  sample  with  a  mix- 
ture of  equal  parts  of  glycerine  and  saturated  magnesiun  sul- 
phate solution.  The  eggs  present  float  to  the  surface  and  can 
be  poured  off  on  large  slides  for  examination.  By  centrifuging 
negative  specimens  and  again  floating  the  eggs  in  a  glycerine-salt 
solution  a  still  higher  percentage  of  positives  can  be  found.  In 
a  test  trial  in  Siam  35.5  per  cent  of  45  faecal  samples  were  found  to 
be  hookworm-infected  by  examination  of  two  slides  by  the  plain 
smear  method,  whereas  84.4  per  cent  were  positive  by  the  exam- 
ination of  a  single  slide  by  the  glycerine-salt  method,  and  86.6 
per  cent  by  examination  of  two  slides. 

A  still  more  accurate  method  is  the  brine  flotation-loop  method 
of  Kofoid  and  Barber.  A  large  faecal  sample  is  thoroughly  mixed 
with  concentrated  brine  in  a  paraffin  paper  container  of  two  or 
three  ounces  capacity.  The  coarse  float  is  forced  below  the 
surface  by  means  of  a  disk  of  No.  9  steel  wool,  and  the  container 
is  allowed  to  stand  an  hour  for  the  eggs  to  float  to  the  surface. 
The  surface  film  is  then  wiped  off  with  wire  loops  one-half  inch 
in  diameter,  the  material  transferred  to  a  large  slide,  and  exami- 
nation made.  The  number  of  positives  escaping  detection  by  this 
method  is  practically  negligible.  Another  very  simple  and  effect- 
ive method  is  to  mix  the  faecal  sample  thoroughly  with  a  con- 
centrated salt  solution  in  a  container  so  filled  that  there  is  a  slight 
meniscus.  After  standing  a  few  minutes  the  eggs  rise  and  adhere 
to  a  glass  slide  touched  to  the  surface  of  the  meniscus.  This 
method  is  very  effective  especially  for  hookworm  eggs,  but  is 
said  not  to  be  useful  for  operculated  eggs  or  for  larvae. 


CHAPTER  Xn 

THE  FLUKES 

General  Account.  —  The  flukes  are  animals  of  a  very  low  order 
of  development  in  some  respects  and  of  very  high  specialization 
in  others.  In  shape  they  are  flat  and  often  leaflike,  with  the 
mouth  at  the  bottom  of  a  sucker  at  the  anterior  end  and  with  a 
second  little  sucker,  for  adhesion,  on  the  ventral  side  of  the  body. 
They  are  all  parasitic  when  adult  and  attach  themselves  to  their 
hosts,  either  externally  or  internally,  by  means  of  their  suckers, 
sometimes  aided  also  by  hooks.  The  development  of  the  ner- 
vous system  is  of  a  very  low  grade,  and  the  only  tendency  towards 
a  brain  is  the  presence  of  a  small  ganglion  at  the  forward  end  of 
the  body  which  gives  off  a  few  longitudinal  nerves.  Sense  organs 
are  almost  lacking  — •  there  is  usually  no  sense  of  sight  and  none 
of  sound;  in  fact  no  sensations  whatever  except  a  meager  sense 
of  touch  falls  to  the  lot  of  these  lowly  animals.  There  is  no  blood 
or  blood  system,  the  result  being  that  the  digestive  tract  and 
excretory  system  are  branched,  often  to  a  surprising  extent,  in 
order  to  carry  food  to  all  parts  of  the  body  and  to  carry  waste 
products  out  from  all  parts.  In  these  respects  the  flukes  are 
very  primitive  animals,  but  in  other  respects  they  equal  or  surpass 
any  other  animals  in  their  complexity.  We  would  have  to  look 
long  to  find  more  intricate  and  highly  specialized  reproductive 
systems  than  they  possess,  and  their  life  histories  are  so  mar- 
velously  complex  as  to  tax  our  credulity.  We  are  accustomed 
to  think  of  a  butterfly  as  having  a  wonderful  life  history  in  that 
it  passes  through  two  phases  of  life,  the  first  as  a  caterpillar,  the 
second  as  a  mature  butterfly,  the  two  being  separated  by  a  third 
inactive  phase  of  existence.  But  by  comparison  with  the  flukes 
this  life  history  appears  simple.  Many  flukes,  especially  those 
which  live  as  internal  parasites  in  the  land  animals,  pass  through 
four  and  sometimes  even  five  distinct  phases  of  existence,  during 
some  of  which  they  are  free-living,  and  during  others  may  para- 
sitize successively  two  or  even  three  different  hosts. 

207 


208  THE  FLUKES 

In  all  flukes  except  those  of  the  family  Schistosomidse  both 
male  and  female  reproductive  systems  occur  in  the  same  individ- 
ual, and  occupy  a  large  portion  of  the  body  of  the  animal.  We 
are  familiar  with  animals  which  appear  to  live  almost  wholly 
to  eat;    the  flukes  are  animals 

which  seem  to  live  merely  for  re-  j^^^  "  ^' 

production.    They  are  reproduc-  ^IWhiS  ' 

tive  machines,  all  the  other  or-  f:f^4^i^^:\Q  ryat.&izi. 

gans  of  their  bodies  being  devel-        WMcmMt^ ^n*- 

oped  only  to  a  sufficient  extent        |»//^^^\t% ^-s- 

to   ensure   the   proper    develop-       |-m3^^M^'rl •3-'* 

ment  and  maturity  of  the  eggs.       I^jK^^H^ctI"  "  ^^ 
The  eggs  proper   and  the  shell      f|Br^^^j5Bgi"~  "*" 
materials  are  produced  by  sepa-      WB^^^^Mm'"  °^' 
rate  glands,  and  sometimes  the      ^K^^^rS^— se^t.V. 
canal  for  conducting  the  sperms       ^^^M^^^'^""^' 

from  another  individual  into  the  ^^j:^^~ ex^.c. 

body  to  fertilize  the  egg  is  distinct 

»             ii      i         1  •   1                1      J.       ii  Fig.  62.     Heterophyes  heterophyes,  a 

from    that    which    conducts    the  ^e^y  small  intestinal  fluke  of  man;    A, 

eggs  out  of  the  body.      The  male  adult;   B  (  X  350),  spines  from   genital 

,                     •  J.        f   4-  ^^'^s;   g-  r.,  genital  ring;   g.  p.,  genital 

system   consists   of   two    or   more  pores;  other  abbrev.  as  in  Fig.  74.    X  33. 

glands  or  testes  for  the  produc-  Egg  shown  above,  x  500.  (After 
tion  of  the  sperms,  two  sperm 

ducts  which  meet  and  enlarge  into  a  "cirrus  pouch"  for  storing 
the  sperms  until  ready  to  be  used,  and  a  rectractile  copulatory 
organ.  All  these  complex  sexual  organs  in  a  single  animal  which 
may  be  no  larger  than  the  head  of  a  pin  (Fig.  62)! 

Almost  as  soon  as  the  fluke  reaches  its  final  host  and  assumes 
its  mature  form,  development  of  the  reproductive  systems  be- 
gins. Although  both  sexes  are  usually  in  the  same  individual, 
mutual  cross-fertilization  generally  takes  place,  the  sperms  of 
two  individuals  simultaneously  fertilizing  each  other.  The  num- 
ber of  eggs  maturing  in  a  single  fluke  is  enormous,  and  while  it 
undoubtedly  varies  in  different  species  and  in  different  individuals, 
the  eggs  are  probably  always  to  be  reckoned  in  the  thousands, 
and  sometimes  in  the  hundreds  of  thousands. 

Life  History.  —  The  life  histories  of  all  the  flukes  which  are 
internal  parasites  have  much  in  common,  and  all  of  them  undergo 
a  series  of  marvelous  transformations  from  egg  to  adult. 

The  fluke  which  is  most  thoroughly  known  in  every  respect 


LIFE  HISTORY  OF  LIVER  FLUKE  209 

is  the  almost  cosmopolitan  liver  fluke,  Fasdola  (or  Distomum) 
hepatica,  of  sheep,  goats  and  other  ruminants.  This  species 
occasionally  establishes  itself  in  man  also,  but  it  can  be  looked 
upon  only  as  an  accidental  parasite  as  far  as  man  is  concerned. 
Its  life  history  (shown  diagrammatically  in  Fig.  63)  will  be 
described  in  some  detail  since  it  is  more  thoroughly  known  than 
is  that  of  most  of  the  flukes,  and  because  it  is  typical  of  the  group. 

The  adult  of  the  liver  fluke  (Fig.  63A)  Hves  normally  in  the 
bile  passages  and  liver  tissue  of  its  host.  About  three  weeks 
after  the  flukes  have  reached  their  destination  in  or  near  the 
liver,  reproduction  commences.  Eggs  (Fig.  63B)  begin  to  pass 
out  through  the  uterus  of  the  fluke,  and  are  carried  by  the  bile 
of  the  host  to  the  intestine  and  thence  out  of  the  body  by  the 
faeces,  a  single  fluke  producing  as  many  as  50,000  eggs.  Since 
there  may  be  over  200  flukes  in  a  single  host,  the  number  of 
eggs  voided  may  amount  to  many  millions.  These  eggs,  if  they 
chance  to  fall  into  water  of  moderate  temperature,  hatch  out 
little  ciliated  embryos  known  as  miracidia  (Fig.  63D),  which 
resemble  ciliated  protozoans.  They  are  about  100  /*  {^^jj  of  an 
inch)  in  length.  Each  of  the  embryos  swims  about  for  a  day  or 
two,  by  means  of  its  cilia,  in  an  effort  to  find  a  suitable  interme- 
diate host,  in  this  case  certain  species  of  snails  of  the  genus 
Limncea  (Fig.  63E),  and  if  successful  it  bores  into  the  snail  by 
means  of  a  little  pimple-like  projection  at  the  anterior  end  of 
the  body.  It  is  obvious  that  only  a  small  per  cent  of  the  embryos 
are  likely  to  survive  the  double  risk  of  not  reaching  water,  and 
if  safely  in  water  of  not  reaching  a  suitable  snail  to  bore  into. 
However,  once  safely  within  the  tissues  of  the  snail,  the  embryo 
begins  the  second  phase  of  its  existence,  during  which  it  reproduces 
to  make  up  for  the  enormous  mortaHty  encountered  in  the  trans- 
fer from  sheep  to  snail. 

In  the  course  of  some  days  the  ciliated  embryo  transforms  into 
a  saclike  body  or  ''sporocyst"  (Fig.  63F),  the  inner  /' germina- 
tive  "  cells  of  which  act  as  parthenogenetic  eggs  {i.e.,  eggs  which 
do  not  need  fertilization),  each  developing  into  a  larva  of  a  new 
type,  known  as  a  redia  (Fig.  63G).  The  latter,  when  nearly 
mature,  burst  the  wall  of  the  mother  sporocyst  and  migrate  into 
other  tissues  of  the  snail.  The  redise  are  very  simple  organisms 
with  a  sucker  and  an  unbranched  blind  pouch  for  a  digestive 
tract.     Like  the  sporocyst  they  contain  germinative  cells  within 


210 


THE  FLUKES 


BCX90) 


Fig.  63.  Life  history  of  liver  fluke,  Fasciola  hepatica;  A,  adult  in  liver  of  sheep; 
B,  freshly  passed  egg;  C,  egg  with  developed  embryo,  ready  to  hatch  in  water;  D, 
ciliated  embryo  in  water,  about  to  enter  pulmonary  chamber  of  snail  (E) ;  F, 
sporocyst  containing  redise;  G,  redia  containing  daughter  redise;  H,  redia  of  2nd 
generation  containing  cercarise;  /,  cercaria;  /,  same,  having  emerged  from  snail 
into  water;  K,  cercarise  encysted  on  blade  of  grass;  L,  cercaria  liberated  from  cyst 
after  ingestion  by  sheep;  M,  young  fluke  developing  in  liver  of  sheep. 


LIFE  HISTORIES  OF  FLUKES 


211 


their  bodies  and  these  develop  into  a  second  generation  of  redise 
(Fig.  63H)  ultimately  escaping  from  a  little  "  hatching  pore  " 
in  the  body  wall  of  the  parent.  In  this  way  even  a  third  genera- 
tion of  redise  may  be  developed,  but  usually  the  second  generation 
of  redise  produce  from  their  germinative  cells  a  new  type  of  larva, 
the  cercaria  (Fig.  631),  quite  different  from  either  the  embryo 
or  the  redia.  The  cercarise  are  furnished  with  a  sucker  and  a 
forked  digestive  tract,  and  have  an  actively  moving  tail.  They 
worm  their  way  out  of  the  body  of  the  snail  in  which  they  were 
developed  and  swim  about  in  the  water  by  means  of  lashing 
movements  of  their  tails  (Fig.  63 J).  Eventually  they  attach 
themselves  to  a  submerged  blade  of  grass  or  aquatic  plant,  lose 
their  tails,  secrete  a  cyst  about  themselves  (Fig.  63K),  and  wait  to 
be  eaten  or  drunk  by  a  sheep  or  a  goat.  When  so  swallowed  the 
cyst  is  dissolved  off  in  the  stomach,  and  the  little  parasite  (Fig.  63L) 
wends  its  way  up  the  bile  duct  to  the  liver,  there  to  begin  again 
the  reproduction  of  eggs  and  start  a  repetition  of  the  entire  cycle. 

Such  is  the  life  history  of  the  liver  fluke.  In  some  flukes  this 
strange  life  is  further  complicated  by  the  invasion  of  a  third  host 
by  the  cercarise.  In  some  fluke  parasites  of  frogs,  for  instance, 
the  redise  inhabit  certain  snails,  while  the  cercarise  inhabit  insect 
larvse,  and  infect  their  ultimate  host  by  being  eaten  with  the 
insects.  Several  human  flukes,  including  the  lung  fluke,  Para- 
gonimus  ringeri  (westermani)  have  a  life  history  of  this  type. 
The  encysted  cercarise  of  the  lung  fluke  are  found  in  the  tissues 
of  several  species  of  fresh-water  crabs  and  in  the  earlier  stages 
are  believed  to  be  parasites  of  a  snail  on  which  the  crabs  feed. 
The  Chinese  liver  fluke,  ClonorcMs  sinensis,  parsisitizes  succes- 
sively a  snail,  a  fish  and  a  mammal. 

In  some  species  of  flukes  daughter  sporocysts  are  formed  in- 
stead of  redise,  and  in  some  the  sporocysts  give  rise  to  cercarise 
directly.  The  known  types  of  life  histories  of  flukes  are  graphi- 
cally shown  by  the  following  diagram,  copied  from  Leiper: 


Host 

Transition 

Intermediate  Host 

Transition 

Host 

Encysted 

Sporocyst 

in  mollusc 

Err 

Miracidium 

Sporocyst. . . 

. . .  Daughter  Sporocyst 

in  crustacean 

(or  ciliated 

Sporocyst. . . 

..  Redise 

CercarisB 

in  insect 

Adult 

embryo) 

Sporocyst. . . 

. .  Redise,  Daughter 

Redise 

in  fish 

on  vegetation 

[  Free-swimming . 

212  THE  FLUKES 

tube  of  an  aquatic  animal,  another  in  the  conjunctival  sac  in 
the  eyes  of  birds. 

The  flukes  which  infest  man  may  be  divided  for  convenience 
into  four  groups,  the  blood  flukes,  the  lung  flukes,  the  liver 
flukes  and  the  intestinal  flukes.  Altogether  over  20  different 
species  have  been  found  in  man,  but  only  those  which  are  com- 
mon or  important  will  be  considered  in  the  following  pages. 

Control.  In  all  known  cases  freshwater  snails  act  as  inter- 
mediate hosts  for  the  flukes  which  infest  man  and  domestic  animals. 
A  practical  and  efficient  method  of  destroying  these  snails  would 
make  the  ultimate  eradication  of  fluke  diseases,  in  spite  of  the 
difficulty  in  treating  them,  a  matter  of  brigher  prospect  than  the 
eradication  of  hookworm  and  other  intestinal  parasites,  in  which 
sanitary  disposal  of  faeces  must  be  relied  upon. 

Recent  experiments  by  Chandler  show  that  copper  salts  exert 
a  powerful  effect  upon  snails,  even  in  very  high  dilution,  appar- 
ently acting  by  inhibition  of  necessary  enzymes.  In  experi- 
ments on  a  number  of  snails  of  six  different  families,  including 
members  of  all  the  families  of  which  species  are  known  to  act  as 
intermediate  hosts  for  pathogenic  flukes,  it  was  demonstrated 
that  copper  sulphate  in  proportions  of  one  part  in  from  500,000 
to  2,000,000  parts  of  water  destroys  the  snails  in  all  cases  within 
48  hours.  From  the  point  of  view  of  expense,  harmlessness 
and  convenience  in  use,  copper  sulphate  is  preferable  to  any  other 
substance  which  has  been  tried  or  suggested  for  destroying  snails. 
In  the  dilute  solutions  which  are  necessary  the  water  is  not  in- 
jured either  for  human  or  animal  consumption,  for  bathing,  or  for 
agricultural  purposes.  It  is  destructive  to  very  few  other  or- 
ganisms in  the  water,  except  algse.  It  is,  however,  injurious  to 
some  species  of  fish,  especially  the  young,  and  its  use  may  be 
objected  to  for  this  reason  in  some  places  where  fluke  diseases 
are  prevalent,  e.g.,  in  oriental  countries,  where  fish  are  extensively 
kept  in  the  snail-infested  waters  and  form  an  important  part  of 
the  native  diet.  The  eggs  of  the  snails  are  not  destroyed  by  the 
copper  salts.  With  government  aid  and  supervision,  the  work 
being  carried  out  under  the  direction  of  scientifically  trained 
men  or  commissions,  it  seems  entirely  possible  that  whole  states 
or  countries,  at  least  in  the  vicinity  of  towns  or  villages,  could  be 
freed  of  human  fluke  diseases. 


BLOOD  FLUKES 


213 


-gljW.C 


-S 


Blood  Flukes 

The  most  important  flukes  parasitic  in  man  are  three  species 
of  Schistosoma  (or  Bilharzia)  which  live  in  the  large  bloodvessels 
of  the  abdominal  cavity. 

Schistosoma  is  one  of  the  few  genera  of  flukes  in  which  the  sexes 
are  separate.  The  relation  of  the  sexes  is  one  of  the  most  remark- 
able in  nature.  The  mature 
male  worm  (Fig.  64)  has  a 
cylindrical  appearance  due  to 
the  fact  that  the  sides  of  the 
flat  body  are  folded  over  to 
form  a  ventral  groove .  In  this 
groove,  projecting  free  at  each 
end  but  enclosed  in  the  middle, 
is  the  longer  and  slenderer  fe- 
male, safe  in  the  arms  of  her 
lord.  While  young  the  sexes 
live  apart,  but  as  soon  as  sex- 
ual maturity  is  attained  they 
couple  together  and  spend  the 
rest  of  their  lives  in  this  man- 
ner. 

Unlike  the  liver  flukes,  the 
blood  flukes  do  not  develop 
great  numbers  of  eggs  all  at 

once,  but  instead  develop  them  Fig.  64.     Blood  fluke,  Schistosoma  fuBrna^ 

one    by   one    and  have   only  a  ^^^^^^j  male  ( $ )  carrying  female  ( 9 )  in 

J.         .      ,,             '^      A.     J.  ventral    groove;    int.,    intestine;    gyn.    c, 

lew  m  the   oviduct  at  any  one  gynecophoric  canal  or  ventral  groove;  m., 

time.      Such  a  method   of   re-  f  °"*^'  ^'  «••  central  sucker,    x  8.     (After 

1        •           •       ^      •!•           1         /.  Looss.) 

production    is   facilitated,    of 

course,  by  the  constant  juxtaposition  of  the  male  and  female 
worms.  The  blood  flukes  live  correspondingly  much  longer  than 
the  liver  flukes,  often  persisting  for  many  years. 

Schistosoma  haematobium.  —  The  most  important  species 
from  the  pathogenic  point  of  view  is  Schistosoma  hoematobium 
(Fig.  64).  This  parasite  is  common  in  the  countries  surrounding 
the  eastern  end  of  the  Mediterranean,  southern  Asia  and  many 
parts  of  Africa,  especially  the  east  coast.     In  Egypt  over  half 


214 


THE  FLUKES 


the  population  is  said  to  be  infected,  and  in  an  examination  of 
54  boys  in  the  village  of  El  Marg,  near  Cairo,  49  were  found 
infected. 

These  flukes,  about  one-half  inch  in  length,  abound  sometimes 
in  hundreds  in  the  abdominal  veins  of  their  host,  living  especially 
in  the  portal  vein  and  its  various  branches.  The  eggs  of  the 
worms,  which  are  oval  with  a  stout  spine  at  one  end  (Fig.  65 A), 
and  about  0.16  mm.  (jJ-q  of  an  inch)  long,  are  carried  to  the  small 
vessels  on  the  surface  of  the  urinary  bladder.  By  means  of  the 
sharp  spine  they  penetrate  to  the  wall  of  the  bladder  and  are 
voided  with  the  urine.  As  the  eggs  enter  the  bladder  they  cause 
a  certain  amount  of  bleeding,  resulting  in  a  bloody  urine.  From 
this  symptom  the  disease  caused  by  infection  with  Schistosoma 
hcematohium   is   often   called    '*  parasitic   hsematuria."      Except 


Fig.  65.  Eggs  of  Schistoma;  A,  terminal  spined  egg  oi  S.  ncematobium  from 
urine;  B,  lateral  spined  egg  of  *S.  mansoni  from  faeces;  C,  egg  of  S.  japonicum,  with 
only  rudiment  of  spine ;  note  developed  embryos  in  all.  X  about  200.  (A  and  B 
after  Looss,  C  after  Leiper.) 


in  severe  infections  no  serious  symptoms  appear,  but  when  nu- 
merous the  worms  cause  much  pain  and  give  rise  to  a  great  va- 
riety of  abnormal  conditions  of  the  bladder.  The  damage  they 
do  is  partly  the  result  of  blocking  of  the  veins,  and  partly  the 
result  of  inflammation  and  bleeding  of  the  bladder  caused  by  its 
penetration  by  the  spined  eggs.  Sometimes  the  kidneys,  ureters 
and  other  urino-genital  organs  are  attacked  and  seriously  affected. 
In  addition  there  can  be  little  doubt  but  that  the  worms  excrete 
poisonous  matter  into  the  blood,  as  practically  all  parasitic  worms 
do  to  some  extent,  and  this  probably  accounts  for  part  at  least 
of  the  anemic  and  debilitated  condition  so  common  in  infected 


LIFE  HISTORY  OF  SCHISTOSOMA  215 

people.  Recent  experiments  by  Fairley  seem  to  corroborate  this 
view.  It  is  reported  that  of  625  British  soldiers  who  became 
infected  with  blood  flukes  in  South  Africa  during  the  Boer  war, 
359  were  still  on  the  sick  list  in  1914  exclusive  of  those  perma- 
nently pensioned.  The  cost  to  the  British  government  for  per- 
manent and  "  conditional  "  pensions  for  these  soldiers  amounted 
to  nearly  S54,000  a  year. 

The  life  history  of  Schistosoma  hcematobium  has  only  recently 
been  worked  out  by  Leiper,  of  the  British  Army  Medical  Corps, 
in  Egypt.  It  was  long  known  that  a  ciliated  embryo  or  mira- 
cidium  developed  inside  the  egg  shells,  even  before  they  left  the 
body  of  the  host,  and  that  these  embryos  hatched  out  and  swam 


B 

Fig.  66.  Egyptian  snaJIs  which  serve  as  intermediate  hosts  for  blood  flukes;  A, 
Bullinus  contortus,  an  intermediate  host  for  Schistosoma  hcematobium;  B,  Planorbis 
boissyi,  an  intermediate  host  for  Schistosoma  mansoni.     (After  Leiper.) 


about  when  the  eggs  were  immersed  in  water,  but  beyoud  this 
point  the  life  history  could  only  be  conjectured  from  analogy  with 
the  liver  fluke.  Leiper,  who  had  already  made  some  investi- 
gations in  regard  to  the  life  history  of  S.  japonicum  in  China, 
worked  on  the  life  history  of  this  species,  chiefly  at  El  Marg, 
near  Cairo,  Egypt.  He  found  that  Schistosoma  embryos  are 
attracted  by  several  species  of  fresh-water  snails  and  that  they 
penetrate  the  bodies  of  three  species,  Bullinus  contortus  (Fig. 
66 A),  B.  dyhowskii  and  Planorbis  boissyi  (Fig.  66B).  Here  they 
undergo  transformation  into  sporocysts,  from  which  daugh- 
ter sporocysts  bud  off  (Fig.  67).  After  leaving  the  mother  cyst 
the  daughter  sporocysts  migrate  into  the  tissue  of  the  liver  and 
grow  rapidly.  They  become  greatly  elongated  and  eventually 
ramify  throughout  the  organ,  so  increasing  its  bulk  and  color 
that  an  infected  snail  can  be  detected  at  a  glance.    The  sporo- 


216 


THE  FLUKES 


cysts  move  by  wriggling  movements,  and  absorb  nourishment 
directly  through  the  body  wall.  When  they  become  over-dis- 
tended with  the  cercariae  developing  within  them  the  wall  ruptures 
and  the  cercariae  are  set  free  in  the  snail.  The  cercariae  are  dis- 
charged from  the  mollusc  in  ''  puffs,"  a  number  being  periodically 
shot  into  the  water. 

Examination  of  molluscs  which  were  collected  in  the  El  Marg 
canal  resulted  in  finding  17  species  of  cercariae,  among  them  the 
cercariae  with  forked  tails  and  no  bulb  in  the  oesophagus,  the 


Fig.  67.  Larval  forms  of  blood  flukes  teased  from  liver  of  Planorbis;  J., 
sporocyst  containing  daughter  sporocysts;  B,  daughter  sporocysts  in  liver  tissue; 
C,  cercaria.  Note  forked  tail,  characteristic  of  Schistosoma  cercariae.  (After 
Leiper.) 


typical  form  of  Schistosoma  cercariae  (Fig.  67C).  Infected  mol- 
luscs may  continue  to  liberate  cercariae  for  several  weeks.  Leiper 
later  found  that  S.  hcematobium  developed  only  in  the  species 
of  Bullinus,  the  cercariae  from  Planorbis  belonging  to  another 
species,    S.    mansoni.     In    Natal    and    the    Transvaal    a    small 


TREATMENT  AND  PREVENTION  OF  SCHISTOSOMA    216a 

dark-colored  snail,  Physopsis  africana,  acts  as  an  intermediate 
host. 

When  fully  developed  the  cercariae  escape  from  the  snails  and 
swim  about  in  water  in  search  of  a  final  host.  They  do  not  live 
at  best  as  long  as  48  hours,  so  a  vast  majority  of  the  larvae  must 
perish  from  failure  to  find  a  suitable  host.  It  has  been  shown 
that  not  only  man  but  also  various  species  of  monkeys  and  ro- 
dents may  be  infected  by  the  cercariae. 

Infection  may  occur  in  two  different  ways:  by  drinking  water 
containing  cercariae,  or  by  bathing  in  it,  since  the  cercariae  are 
able  to  penetrate  either  the  mucous  membranes  or  the  sound 
skin,  migrating  through  the  body  until  they  reach  their  desti- 
nation in  the  abdominal  veins.  The  natives  of  some  parts  of 
Africa  realize  that  infection  may  result  from  bathing,  but  from 
the  nature  of  the  disease  they  believe  that  infection  takes  place 
by  way  of  the  urinary  passages  and  therefore  employ  various 
mechanical  devices  to  prevent  infection  in  this  manner.  There 
is  little  doubt,  when  infection  occurs  from  drinking  water,  that 
the  cercariae  adhere  to  the  walls  of  the  mouth  and  throat  and  bore 
through  them,  since  passage  through  the  acid  juices  of  the  stom- 
ach is  apparently  fatal  for  them. 

The  disease  usually  develops  in  from  two  to  four  months  after 
infection. 

Treatment  and  Prevention.  —  Recent  work  by  Christopherson 
has  shown  that  tartar  emetic  has  a  specific  action  on  both  the 
worms  and  the  eggs,  and  leads  to  a  rapid  improvement  in  the 
condition  of  the  infected  individuals.  The  drug  is  given  in  the 
form  of  intravenous  injections  on  alternate  days  beginning  with 
J  grain  in  40  to  50  minims  of  saline  solution,  and  increasing  the 
dose  by  |  grain  with  each  injection  until  a  dose  of  2  to  2 J  grains 
is  reached  The  injections  are  continued  until  all  of  the  voided 
eggs  are  sterile  and  show  evidence  of  deterioration.  Usually  the 
total  amount  of  tartar  emetic  required  is  between  20  and  30 
grains.  Christopherson's  work  has  been  confirmed  by  a  number 
of  other  investigators.  The  dead  eggs  imbedded  in  the  tissues  may 
continue  to  cause  inflammation  for  a  time,  but  the  symptoms 
gradually  disappear.  Even  without  reinfection  some  of  the 
worms,  if  the  disease  is  left  untreated,  may  continue  to  live  and 
produce  eggs  for  years,  but  in  most  longstanding  cases  reinfec- 
tion probably  occurs  frequently. 


216b  the  flukes 

Now  that  the  life  history  and  modes  of  infection  are  known, 
definite  preventive  measures  can  be  taken.  Prevention  of  con- 
tamination of  drinking  water  by  infected  urine  is,  of  course,  the 
ideal  preventive  measure,  but  in  countries  where  the  disease  is 
most  prevalent,  as  in  Egypt,  cooperation  of  the  natives  in  such 
a  matter  is  more  than  can  be  expected.  Leiper  has  pointed  out, 
however,  that  the  disease  can  be  eradicated  without  such  coop- 
eration by  other  means,  depending  upon  local  conditions.  In 
large  towns  and  cities  it  is  practical  to  destroy  the  free-swim- 
ming infective  stage  of  the  worm  by  filtering  or  impounding 
water,  while  in  rural  districts  the  worm  must  be  deprived  of 
its  intermediate  host.  Cairo,  for  example,  obtains  its  water 
supply  from  the  Nile,  part  of  it  being  unfiltered.  Water  used 
for  irrigation  purposes  above  Cairo,  and  frequently  contaminated, 
is  turned  back  into  the  river  and  is  probably  the  chief  source  of 
infection  at  Cairo,  where  10,000  children  are  said  to  become  in- 
fected annually.  In  towns  where  filtering  is  impractical  the 
water  could  be  rendered  uninfective  by  impounding  it  in  protected 
reservoirs  for  48  hours,  since  the  cercarise  die  in  this  time.  The 
objection  to  this  is  that  the  water  loses  valuable  sediment,  but 
it  is  doubtful  whether  the  agricultural  loss  from  lowered  vitality 
resulting  from  Schistosoma  infection  is  not  greater  than  is  the 
loss  in  fertility  from  impounding  water. 

It  seems  very  probable  that  the  use  of  copper  sulphate  for 
destroying  snails  in  ponds  or  irrigation  ditches  in  agricultural 
districts,  as  outlined  on  p.  211,  will  prove  to  be  an  effective  means 
of  controlling  the  disease.  At  present  a  preventive  measure  used 
in  Egypt  is  the  intermittent  flow  of  water  in  irrigation  canals, 
under  government  control.  The  snails  which  serve  as  inter- 
mediate hosts  for  Schistosoma  are  said  to  die  if  the  water  in  which 
they  live  is  dried  up.  It  is  customary  for  water  to  be  turned  out 
of  most  irrigating  canals  for  periods  of  15  days  at  a  time,  which 
Leiper  says  would  be  sufficient  to  destroy  molluscs  in  them  except 
in  puddles  left  by  an  uneven  floor,  which  must  be  treated  by 
chemicals,  or  the  floors  leveled.  However,  in  view  of  the  remark- 
able resistance  which  most  snails  have  to  drouth  and  to  other 
adverse  conditions,  this  conclusion  ought  to  be  proven  by  eirtensive 
experimentation.     Infected  water  to  be  used  for  washing  can  be 


OTHER  SPECIES  OF  SCHISTOSOMA  217 

rendered  non-infective  by  the  addition  of  one  part  of  cresol  in 
10,000  parts  of  water. 

Leiper's  work  shows  that  transient  collections  of  water  are  not 
sources  of  infection  after  recent  contamination,  whereas  all  per- 
manent collections  of  water,  as  in  rivers,  canals  and  marshes, 
are  dangerous  if  inhabited  by  a  suitable  intermediate  host. 
The  removal  of  infected  persons  from  a  given  body  of  water 
would  have  no  immediate  effect  in  reducing  its  infectiveness, 
since  the  snails  discharge  cercarise  into  the  water  for  a  prolonged 
period.  The  preventive  measures  briefly  outlined  above  were 
worked  out  by  Leiper  for  the  special  conditions  existing  in  the 
infected  parts  of  Egypt  but  in  a  broad  way  they  are  applicable 
wherever  Schistosoma  hcematohium  occurs. 

Other  Species.  —  There  are  two  other  species  of  Schistosoma 
which  are  pathogenic  to  man.  One,  S.  mansoni,  was  long  con- 
fused with  >S.  hcematohium,  the  only  apparent  differences  having 
been  observed  in  the  eggs.  The  eggs  of  S.  mansoni  (Fig.  65B) 
are  provided  with  a  lateral  instead  of  a  terminal  spine,  and  are 
voided  in  the  digestive  tract  and  its  appendages,  whence  they  are 
liberated  with  the  faeces,  instead  of  making  an  exit  from  the  body 
by  way  of  the  urinary  organs.  By  experimental  infections  of 
mice  Leiper  showed  that  cercarise  from  the  snail  Planorhis  hoissyi 
(Fig.  66B)  developed  into  worms  somewhat  smaller  than  those 
from  the  species  of  Bullinus,  with  certain  distinct  differences  in 
anatomy.  The  cercariae  from  Planorhis  produced  only  lateral- 
spined  eggs  which  were  voided  with  the  faeces,  thus  showing  that 
S.  mansoni  was  really  a  distinct  species  and  not  merely  an  abnor- 
mal type  of  S.  hcematohium.  This  parasite  occurs  in  common  with 
the  foregoing  species  in  many  parts  of  Africa  and  is  also  common 
in  the  West  Indies,  Venezuela  and  perhaps  other  parts  of  tropi- 
cal America.  Like  the  hookworm,  it  was  probably  introduced 
from  Africa  in  the  slave  days.  The  intermediate  host  in  Ven- 
ezuela has  recently  been  shown  by  Iturbe  and  Gonzales  to  be 
the  snail  Planorhis  guadelupensis,  whereas  in  Brazil  Lutz  has 
shown  P.  olivaceus  to  be  the  intermediate  host. 

The  anemia  and  debility  caused  by  S.  mansoni  is  similar  to  that 
caused  by  S.  hcematohium.  The  irritation  and  inflammation  of 
the  urinary  organs  is  replaced,  however,  by  similar  symptoms  of 
the  intestine,  and  a  kind  of  dysentery  often  results. 

The  manner  of  transmission  of  the  parasite  is  similar  to  that 


218  THE  FLUKES 

of  Schistosoma  hcematohium  except  that  infected  faeces  instead  of 
urine  contaminates  water  inhabited  by  a  suitable  intermediate 
host,  as  Planorhis  hoissyi. 

A  third  species  of  Schistosoma,  S.  japonicum,  is  endemic  in 
parts  of  Japan,  China  and  the  PhiHppine  Islands,  and  perhaps 
in  many  other  oriental  countries.  It  is  slightly  smaller  than 
the  other  species  (about  two-fifths  of  an  inch  in  length)  and  pro- 
duces eggs  (Fig.  65 C)  which  do  not  have  the  spine  that  is  so 
characteristic  of  the  other  species  of  Schistosoma,  but  only  a 
rudiment  in  the  form  of  a  little  lateral  knob.  The  eggs  of  S. 
japonicum,  like  those  of  S.  mansoni,  are  voided  from  the  intestine 
with  the  faeces.  They  also  frequently  become  lodged  in  the 
liver  gall  bladder,  walls  of  mesenteric  bloodvessels,  spleen,  pan- 
creas, and  sometimes  other  organs,  not  even  the  brain  being 
exempt.  The  female  worm  must  in  some  way  deposit  her  eggs 
outside  the  bloodvessel  in  which  she  lives  since  they  are  ap- 
parently carried  to  their  destination  by  the  lymph  streams. 
Severe  infections  with  this  parasite  usually  prove  fatal  sooner  or 
later,  and  post-mortem  examinations  show  many  of  the  organs 
of  the  body  to  be  badly  affected.  Infection  with  S.  japonicum 
is  associated  with  a  skin  disease  known  to  the  natives  as  "  ka- 
bure,"  and  probably  caused  by  the  burrowing  of  the  cercariae 
in  the  skin.  According  to  Laning  of  the  U.  S.  Navy,  it  is  not  an 
uncommon  thing  for  large  per  cents  of  the  crews  of  patrol  gun- 
boats in  the  Yangtze  River  to  be  completely  disabled  by  infection 
with  this  parasite.  Laning  divides  the  disease  caused  by  S, 
japonicum  into  three  stages.  The  first  stage,  lasting  from  three 
to  six  weeks,  is  marked  by  high  afternoon  temperatures,  slow 
pulse,  respiratory  troubles,  transient  oedema  and  rash  on  the 
skin  and  mucous  membranes,  abdominal  pains,  digestive  irregu- 
larities and  sometimes  mental  disturbances.  The  second  stage 
is  marked  by  enlarged  liver  and  spleen,  dysenteric  symptoms, 
anemia  and  irregular  fever.  The  third  stage,  which  does  not 
always  occur,  but  may  appear  in  from  three  to  five  years  where 
there  are  constant  reinfections,  is  marked  by  diseased  liver, 
oedema  of  legs  and  arms,  emaciation,  anemia  and  dysentery, 
and  death  from  exhaustion  is  not  uncommon. 

The  life  history  and  mode  of  infection  in  the  case  of  S.  japonicum 
is  undoubtedly  very  similar  to  that  in  other  species  of  Schistosoma. 
Miyairi,  a  Japanese  investigator,  found  reproductive  stages  of 


LIFE  HISTORY  OF  SCHISTOSOMA  JAPONICUM  219 

S.  japonicum  in  a  species  of  Ldmncea  in  Japan.  Miyairi  and 
Suzuki,  in  further  work  on  the  Hfe  history  of  this  fluke,  found 
that  after  sporocysts  have  developed  in  the  tissues  of  infected 
snails  redise  are  produced,  50  or  more  from  each  sporocyst. 
The  long,  coiled  rediae  crowd  the  liver  and  produce  cercariae,  the 
latter  reaching  maturity  in  about  seven  weeks.  If  in  autumn 
the  cercarise  have  become  fully  developed  but  have  not  left 
the  snails  they  remain  in  their  hosts  over  winter. 

Leiper  obtained  development  of  the  characteristic  fork-tailed 
cercarise  in  another  small  snail,  Blanfordia  (or  Katajama)  noso- 
phora,  common  in  the  rice  fields  of  Japan.  There  is  an  interest- 
ing tale  connected  with 
Leiper's  experiments  on 
infection  with  these  para- 
sites. With  great  care  this 
investigator  experimented 
with  the  infection  of  snails 
which  he  had  imported 
from  Japan  to  work  on  in 
his  laboratory  at  Shanghai. 
After  having  succeeded  in 
obtaining  infection  of  the 
snails,  he  teased  out  the 
livers  in  water  to  liber- 
ate the  cercarise.  Four 
laboratory-bred    mice, 

which   are   difficult  to  ob-         Fig.  68.     Mesentery  of  mouse   with   blood- 
tain    in    the    Orient,    were    r'^^^\   ^^^^"^^^     ^^*^      Schistosoma.       (After 
'  Leiper.) 

immersed    in    the    water 

in  which  the  cercarise  had  been  liberated,  and  a  start  was  made 
for  England.  But  alas!  a  woman  in  a  neighboring  stateroom 
objected  to  the  presence  of  the  mice  so  near  and  demanded  their 
relegation  to  the  butcher's  cabin,  where  three  of  them  died.  At 
Aden  the  few  remaining  infected  molluscs  were  sacrificed  and 
the  last  mouse  was  subjected  to  infection.  A  month  later  when 
the  animal  was  examined  in  the  laboratory  of  the  London  School 
of  Tropical  Medicine  many  blood  flukes,  males  and  females  in 
couples,  were  found  in  the  portal  bloodvessels  (Fig.  68). 

It  should  be  remarked  in  concluding  this  discussion  of  the 
blood  flukes  that  many  snails,  including  members  of  the  genera 


220  THE  FLUKES 

Planorbis  and  Limncea,  which  could  very  probably  act  as  inter- 
mediate hosts  as  well  as  the  species  in  which  the  development 
has  actually  been  observed,  are  abundant  in  the  United  States, 
and  there  is  great  danger  that  if  once  introduced,  at  least  in  the 
warmer  parts  of  the  country,  these  blood  flukes  might  become 
endemic.  Careful  examination  of  immigrants  from  endemic 
countries  and  exclusion  of  Schistosoma-irSected  persons  is  impor- 
tant if  the  infection  is  to  be  kept  from  becoming  established. 
An  ounce  of  prevention  in  this  country  is  worth  a  pound  of  cure. 

Lung  Flukes 

In  Japan,  China,  the  Phihppines,  and  other  oriental  countries, 
a  region  which  seems  to  be  particularly  afflicted  with  fluke  dis- 
eases, there  occurs  a  very  serious  lung  disease  caused  by  a  species 
of  fluke,  Paragonimus  ringeri  (westermani)  (Fig.  69).     It  is  also 


ut,.4 


Fig.  69.     Lung  fluke,  Paragonimus  ringeri.     Abbreviations  as  in  Fig.  74. 
X  about  7.     (Partly  after  Looss,  partly  after  Leuckart.) 

found  in  dogs.  In  some  parts  of  Formosa  fully  50  per  cent  of 
the  population  is  infected.  A  closely  alHed  species,  P.  kellicotti, 
occurs  in  hogs  in  the  United  States,  and  probably  in  other  parts 
of  the  world. 

The  lung  fluke  is  about  half  an  inch  in  length,  reddish  brown 
in  color,  and  relatively  very  broad.  The  adult  lives  most  fre- 
quently in  the  lungs  of  its  host,  where  it  produces  cavities  an 
inch  or  two  in  diameter.     The  cavities  become  filled  with  various 


LUNG  FLUKES 


221 


Fig.  70.  Eggs  of  lung  fluke  in 
contents  of  cyst  in  lung  of  hog.  X 
about  50.     (After  Stiles  and  Hassall.) 


tissues  through  which  the  parasite  tunnels  out  its  burrows  and 
in  which  it  deposits  its  eggs  (Fig.  70).  These  excavations  in  the 
lung  connect  with  the  bronchial  tubes,  through  which  the  blood, 
parasite  eggs  and  other  products  are  voided,  thus  causing  the 
characteristic  blood-spitting.  The 
expectorations,  resembling  those 
of  pneumonia,  are  of  a  pecuUar 
brownish  red  color,  due  in  part 
to  the  blood  corpuscles  present 
and  in  part  to  the  dark  brown 
fluke  eggs,  which  are  often  very- 
abundant. 

Occasionally  the  lung  fluke  bur- 
rows in  other  organs  and  glands 
of  the  body,  such  as  the  liver, 
spleen,  muscles,  intestine  and 
brain.  Musgrave  found  in  the  Philippines  that  sometimes  many- 
parts  of  the  body  are  infested  at  once,  and  in  one  case  he  found 
over  a  hundred  mature  parasites  in  a  muscular  abscess.  When 
they  burrow  in  the  brain  they  cause  epileptic  fits  and  usually  in 
time  cause  death. 

The  eggs  of  the  lung  fluke  (Fig.  71  A)  when  immersed  in  fresh 

water  for  several  weeks  develop 
within  themselves  typical  ciliated 
embryos  or  miracidia  (Fig.  71B). 
The  latter  burst  away  the  little 
cap  at  the  end  of  the  egg  and 
emerge  as  free-living  animals. 

Nakagawa  has  recently  shown 
that  if  these  miracidia  are  placed 
in  water  with  certain  species  of 
snails,  particularly  Melania  liher- 
tina,  the  miracidia  swarm  about  the  snails  and  burrow  into  them, 
shedding  their  cilia  as  they  go.  The  entire  cycle  of  development 
in  the  snail  has  not  been  worked  out  but  it  is  probably  very  similar 
to  that  of  Schistosoma.  Sporocysts  of  various  sizes  occur  in  the 
liver  and  other  tissues  of  the  snail,  and  it  is  probable  that  these 
produce  the  cercariae  directly. 

Nakagawa  discovered  the  encysted  cercarise  of  this  species, 
proved  to  be  such  by  experimental  infection  of  animals,  in  three 


Fig.  71.  A,  freshly  passed  egg 
of  lung  fluke;  B,  egg  of  lung  fluke 
with  fully  developed  embryo.  X 
250.     (After  Katsurada.) 


222 


THE  FLUKES 


species  of  crabs  in  Formosa,  and  Yoshida,  another  Japanese  in- 
vestigator, acting  on  the  discovery  of  his  countryman,  found  the 
larvffi  in  a  fourth  species  of  crab  in  Japan.  The  crabs  most  com- 
monly infected  are  Potamon  ohtusipes,  a  coarse-shelled,  chestnut- 
colored  crab  about  one  and  a 
half  inches  in  diameter,  and 
P.  dehaanii,  a  slightly  smaller 
,^,     .  ^^     ^    ^^^  species,  grayish  black  or  red- 

^^&^^P^    dish    in    color.      Both    these 
>':'<^/iii^^^^^%      ^^^t)S    bound   in   the   shallow 
waters  of  mountain   streams, 
and    the    former    species    is 
sometimes  used  as  food.    An- 

FiG.  72.  A  common  fresh-water  crab  other  implicated  SpecieS, 
of  Japan,  Eriocheir  japonicus,  which  serves  jH^rrochcir  idVOTlicU^  TFis"  72^ 
as  a  host  for  lung  fluke.     (After  Yoshida.)     .  i  •        n     i 

IS  abundant  m  all  plams  rivers 
in  Japan  and  is  a  common  article  of  diet  throughout  the  country. 
It  is  a  larger  crab,  reaching  a  diameter  of  three  inches,  and  has 
large  hairy  claws.  The  fourth  species,  Sesarma  dehaani,  is  of 
medium  size,  dark  in  color  with  light  reddish  claws,  and  inedible. 
Miyairi  has  shown  that  in  Korea  another  crab,  Astacus  japonicus, 
is  the  intermediate  host. 

The  lung  fluke  cercarise  encysted  in  these  crabs  (Fig.  73A) 
were  found  chiefly  in  the  liver  while  young,  but  when  older  they 

OS. 

ex.v, 

Fig.  73.  A,  encysted  cercaria  of  human  lung  fluke,  Paragonimus  ringeri,  from 
gill  of  crab;  B,  larva  emerging  from  cyst.  o.  s.,  oral  sucker;  int.,  intestine;  ex.  v., 
excretory  vesicle;  v.  s.,  ventral  sucker.      X  50.     (After  Yoshida.) 

occur  in  the  gills.  They  vary  in  number  from  a  few  to  several 
hundred.  In  some  localities  a  very  high  per  cent  of  crabs  are 
infected,  Nakagawa  reporting  that  practically  100  per  cent  are 
infected  in  one  district  in  Formosa  where  the  lung  fluke  is  very 
common.  The  cysts  containing  the  cercarise  are  nearly  round, 
0.5  mm.  (sV  of  an  inch)  or  less  in  diameter,  and  have  relatively 


LUNG  FLUKES  223 

thick  walls.  The  enclosed  cercaria  lies  straight,  unlike  most 
encysted  cercariae,  and  the  body  is  entirely  covered  by  short 
spines.  In  fully-developed  specimens  the  suckers,  digestive 
tract  and  other  parts  of  the  anatomy  of  the  enclosed  cercarise  can 
be  seen  (Fig.  73 A) .  While  still  in  the  cysts  the  cercariae  are  fairly 
resistant  to  unfavorable  environmental  influences,  but  are  easily 
destroyed  after  hatching. 

When  an  encysted  cercaria  is  swallowed  by  a  susceptible  ani- 
mal the  cyst  wall  is  dissolved  off  in  the  intestine,  the  active 
liberated  larva  (Fig.  73B)  bores  through  the  intestinal  wall, 
wanders  about  in  the  abdominal  cavity  for  some  time,  then 
bores  through  the  diaphragm  into  the  pleural  cavity,  whence  it 
eventually  penetrates  the  lungs  from  the  outer  surface.  It 
becomes  mature  in  about  90  days.  Occasionally  the  worms 
apparently  get  lost  and  bore  through  the  abdominal  wall  and 
muscular  connective  tissues.  It  is  probably  in  this  way  that 
other  organs  than  the  lungs  are  penetrated  by  the  flukes. 

There  are  two  ways  in  which  man  may  become  infected,  namely, 
by  eating  infected  crabs  which  are  not  thoroughly  cooked,  or 
by  drinking  water  containing  cysts  discharged  from  infected 
crabs.  As  already  remarked,  the  mature  cysts  make  their  way 
to  the  gills,  whence  they  can  easily  be  removed,  and  whence 
they  probably  escape  readily  under  natural  conditions,  thus 
becoming  free  in  the  water.  Here  they  may  remain  alive  for 
some  time,  probably  30  days  or  more.  Yoshida  states  that  the 
cysts  sink  to  the  bottom,  in  which  case  human  infection  could 
occur  only  rarely  if  ever  from  infected  water.  Nakagawa,  how- 
ever, observed  that  20  per  cent  of  the  larvae  when  freed  float 
on  the  surface  of  the  water. 

Prevention  of  infection  consists  either  in  the  destruction  of  the 
snails  which  act  as  the  first  intermediate  host  by  the  use  of  copper 
sulphate,  as  outlined  on  p.  211,  or  by  abstinence  from  the  use  of 
raw  crabs  as  food  and  in  avoidance  of  water  for  drinking  which 
may  possibly  be  infected.  Whether  or  not  other  animals  may 
serve  as  hosts  for  the  cercariae  is  unknown,  but  if  the  allied  Para- 
gonimus  kellicotti  is  truly  endemic  in  the  United  States,  where  no 
fresh-water  crabs  are  found,  some  other  animal  must  serve  as  an 
intermediate  host,  possibly  certain  species  of  crayfish.  The  fact 
that  the  lung  fluke  is  not  known  as  an  endemic  human  parasite  in 
this  country  suggests  that  the  intermediate  host  may  be  an  animal 


224 


THE  FLUKES 


which  is  not  used  as  food  and  the  habits  of  which  give  Httle  oppor- 
tunity for  the  parasites  to  gain  access  to  the  human  body.  The 
disease  is  said  to  have  increased  in  Peru,  having  been  introduced 
there  by  Japanese  and  Chinese  laborers.  If  this  is  true  some 
Peruvian  animal,  probably  a  fresh-water  crab,  must  serve  as  an 

intermediate  host.  This  suggests  that 
the  disease  if  once  introduced  might 
flourish  in  other  countries,  especially 
where  fresh-water  crustaceans  are  eaten. 
Lung  fluke  infection  is  evidently  an- 
other disease  for  which  a  quarantine 
should  be  established. 

Liver  Flukes 

Although  the  liver  fluke  of  the  sheep, 
Fasciola  hepatica,  and  other  flukes  of 
herbivorous  animals  are  occasionally 
found  in  man,  they  cannot  be  looked 
upon  as  usual  human  parasites.  Adult 
liver  flukes  are  sometimes  accidentally 
eaten  with  raw  liver,  in  which  case 
they  attach  themselves  to  the  mem- 
branes of  the  throat,  causing  irritation, 
congestion,  a  buzzing  in  the  ears, 
difficult  breathing,  and  other  quite 
no.  74.  The  chin'II^  fluke,  alarming  symptoms  Vomiting  to  ex- 
Clonorchis     sinensis.      X  3|.  pel  the  worms  usually  gives  immediate 

m.,  mouth  in  oral  sucker;  ph.,  pplJAf 

pharynx;  gen.  p.,  genital  pores;  '  . 

V.  s.,  ventral  sucker;  sh.  gl.,  so-  There  are  Several  species  of  flukes, 
called  vitteiiine  or  yolk  glands  however,    which   are    apparently   espe- 

really  shell  glands;   ut.,  coiled  '  ...  ^ 

egg-filled  uterus;  int.,  intestine;  cially  adapted  for  parasitizmg  carnivo- 
sp.  d.,  sperm  duct;  ov.,  ovary;  j.^^^  animals,  and  which  are  common 

sem.   rec,   seminal   receptacle,  .  . 

where  sperms  for  fertilizing  eggs  human  parasites  m  some  countries. 
aretemporariiy8tored;t.,testis;  Japan,  China,  the  Philippines  and  other 

Gxc.  C.J  GxcrGiiory  CRiiBdj  cxc.  p») 

excretory  pore.    (After  Stiles.)  Oriental  countries  are  especially  aflflicted 

by  these  flukes.  The  commonest  species 
in  man  is  the  Chinese  fluke,  Clonorchis  sinensis  (Fig.  74)  which 
is  found  in  all  of  southern  Asia  from  India  to  Korea.  In  some 
parts  of  Japan  about  60  per  cent  of  the  population  are  said  to 
harbor  it  in  their  livers,  sometimes  in  hundreds  or  even  thousands. 


LIVER  FLUKES 


225 


-TTV.**"  1/ 

. ._ int.- m 


ut- 


-ahflfc- 


— -noisizr- 


>«CC. 


In  some  districts  in  Korea  80  per  cent  of  the  inhabitants  are  said 
to  be  infected.  Leiper  found  it  common  in  both  dog  and  man  in 
the  vicinity  of  Shanghai.  It  is  also  found  in  the  liver  ducts  of  cats, 
hogs,  and  probably  other  flesh-eating  animals.  It  is  from  one-half 
to  three-quarters  of  an  inch  in  length,  and  nearly  four  times  as  long 
as  wide.  The  ventral  sucker  is  very  small,  and  is  situated  on  the 
anterior  third  of  the  body.  Some  authors  believe  that  a  small 
variety  of  this  fluke  found  in  Japan  constitutes  another  species, 
C.  endemicus,  but  this  view  is  assailed  by  recent  investigations. 
In  Europe  there  occurs 
a  species,  Opisthorchis 
felineus  (Fig.  75A), 
which  is  very  common 
in  domestic  cats  and 
dogs  and  is  by  no  means 
uncommon  in  man; 
there  is  one  record  of  its 
having  been  found  in 
eight  or  nine  out  of  124 
post  mortem  examina- 
tions in  Siberia.  A  very 
closely  related  species, 
0.  pseudofelineus  (Fig. 
75B),  has  been  found  in 
cats  and  coyotes  in  the 
central  parts  of  the 
United  States.  From 
its  similarity  to  the  Old 
World  species  it  would 
not  be  surprising  to  find 
it  occasionally  parasitic 
in  man. 


B 


rp,       -J-,  .  FiQ.  75.     A,  Cat  fluke,  Opisthorchis  felineus; 

i  ne  JiiUropean  species,   B,  American  cat  fluke,  O.  pseudofelineus.     Abbre- 
viations  as  in   Fig.   74.      x  about  5.     (A,  after 


Stiles  and  Hassall;  B,  after  Stiles.) 


Opisthorchis  felineus^  is 
usually  a  little  less  than 
half  an  inch  in  length,  and  shaped  very  much  like  Clonorchis 
sinensis.  The  American  0.  pseudofelineus  is  somewhat  longer 
and  slenderer  than  the  European  species.  Another  species  of 
the  same  genus,  0.  noverca,  occurs  commonly  in  pariah  dogs 
in  India,  and  occasionally  in  man.  It  differs  from  the  Euro- 
pean species  chiefly  in  having  the  skin  thickly  beset  with  spines. 


226 


THE  FLUKES 


Little  is  known .  of  the  life  history  of  any  species  except  the 
Chinese  fluke,  C.  sinensis.  The  eggs  (Fig.  76A)  are  of  charac- 
teristic shape,  and  hatch  in  water  into  miracidia  (Fig.  76B). 
The  encysted  cercarise  of  this  fluke  (Fig.  77A)  have  been  found 

in  the  subcutaneous  tissues  and 
muscles  of  12  different  species 
of  fresh- water  fish.  The  cysts, 
which  are  very  small,  measuring 
only  about  0.14  by  0.10  mm.  (^ 
by  250  of  an  inch),  are  usually 
more  abundant  in  the  superfi- 
FiG.  76.    Egg  and  ciliated  em-  cial    than    in    the    deeper    tissues. 

bryo  of  Chinese  fluke,  (^ Monorchia  a  ^.Y.r...^U  pv'^f^  po^.  Kp  fniinH  in 
sinensis.    X  700.   (After  Katsurada.)    ^^^^"OUgn     CySlS    Can     De    lOUUQ    m 

fish  throughout  the  year,  the 
younger  ones  are  more  frequently  met  with  in  late  summer  and 
early  autumn. 

When  infecte     fish  are  eaten,   according  to  experimenrs  re- 
cently made  with  animals  by  Kobayashi,  the  larval  flukes  escape 
from  the  cysts  (Fig.  77B)  within  three  hours,  and  in  fifteen  hours 
they      may      already      have 
reached  the  bile  duct  and  gall 
bladder.      The  parasites  reach 
maturity  and  eggs  are  found 
in  the  faeces  of  the  host  within 
26  days.       The  young  flukes 
have    a    spiny    cuticle    until 
nearly  mature,  but  the  spines 
finally  disappear. 

Muto  recently  found  cer- 
carise in  the  snail  Bythinia 
striatula  var.   javonica  which  ^""^"^  ^^^^'  ™"  "^^^^^  ^"^  ^'"''^  sucker;  v.  s., 

.  v?ntral    sucker;    ex.   v.,   excretory  vesicle; 

encyst      m      fish      of     various   ph.,  pharynx;  int.,  intestine. 

species.      When     these     fish 

are  fed  to  dogs  and  mice,  infection  with  Clonorchis  sinensis  results. 
On  the  other  hand,  controls  fed  with  fish  parasitized  by  cercarise 
from  the  snail  Melania  lihertina,  which  Kobayashi  believed  to  be 
the  first  intermediate  host,  developed  infections  with  Meta- 
gonimus  only.  Sporocysts  develop  in  Bythinia  about  three  weeks 
after  infection  with  the  miracidia. 

It  is  probable  that  the  European  liver  fluke,  0.  felineus,  and  its 


Fig.   77.     Larvse  of  Chinese  fluke;  A, 
cercaria  encysted  in  fish;   B,   larva  freed 


LIVER  FLUKE  DISEASE  227 

Indian  and  American  allies  all  have  histories  very  similar  to  that 
of  the  oriental  species.  Their  occurrence  in  man  in  countries 
where  fresh-water  fish  is  a  common  article  of  diet,  and  their 
frequency  in  animals  which  eat  raw  fish,  strongly  suggest  fishes 
as  intermediate  hosts. 

These  liver  flukes,  like  the  sheep  fluke,  live  chiefly  in  the  gall 
bladder  and  bile  ducts  where  they  often  cause  much  mechanical 
obstruction  on  account  of  their  large  numbers.  Severe  infections 
such  as  occur  in  countries  like  Japan  where  raw  fish  is  commonly 
eaten  cause  symptoms  of  a  very  serious  nature.  One  of  the  most 
prominent  of  these  is  enlargement  of  the  liver  accompanied  by 
more  or  less  bloody  diarrhea;  the  latter  becomes  more  and  more 
constant  as  time  goes  on.  The  liver  sometimes  becomes  pain- 
ful, and  jaundice  is  a  frequent  symptom.  The  patient  becomes 
anemic,  emaciated  and  weak,  and  is  ready  prey  for  other  diseases. 
There  are  often  periods  of  partial  recovery  followed  by  relapses, 
probably  due  to  reinfections,  and  the  patient  ultimately  becomes 
exhausted  and  succumbs  to  a  cold,  an  attack  of  malaria,  or  other 
ailment  from  which  one  would  ordinarily  recover  readily. 

There  is  no  specific  treatment  for  the  disease.  The  only  meas- 
ures that  can  be  taken  are  to  remove  the  patient  from  any  possible 
source  of  reinfection  and  to  keep  him  in  the  best  possible  general 
health,  with  wholesome  diet,  good  air  and  proper  exercise.  How 
long  the  flukes  persist  in  the  liver  is  not  known. 

Means  of  prevention  of  the  disease  are  suggested  by  what  is 
known  of  the  life  history  of  the  parasites.  The  most  important 
measure  is  unquestionably  the  suppression  of  the  habit  of  eating 
uncooked  fish  in  places  where  the  disease  is  endemic.  Kobayashi 
has  shown  that  while  the  larvae  of  C.  sinensis  are  killed  at  once  on 
exposure  to  a  boiling  temperature  and  in  a  short  time  when  ex- 
posed to  considerably  lower  temperatures,  they  are  not  de- 
stroyed by  exposure  to  vinegar  for  five  hours,  nor  by  refrigeration. 

Much  could  also  be  done  by  destroying  the  snails  which  act  as 
the  first  intermediate  hosts  by  means  of  copper  sulphate,  as  sug- 
gested on  page  211.  Another  measure,  which  is  far  less  reliable, 
is  the  prevention  of  contamination  of  water  in  which  fish  live.  It 
is  impossible  to  prevent  some  contamination  of  water  by  the  lower 
animals  which  carry  the  infection,  and  it  is  nearly  as  difficult  to 
prevent  contamination  by  human  faeces.  The  almost  universal 
use  of  night  soil  (human  faeces)  for  fertilizer  in  oriental  countries 


228  THE  FLUKES 

is  a  serious  hindrance  to  the  sanitary  disposal  of  such  infected 
material.  Leiper  suggests  that  this  problem  may  be  solved  by  a 
chemical  treatment  of  night  soil  which  would  destroy  all  parasite 
eggs  or  cysts  and  yet  not  injure  its  value  as  a  fertilizer. 

Intestinal  Flukes 

There  are  several  species  of  flukes  which  appear  to  be  common 
parasites  of  the  human  intestine  in  certain  parts  of  the  world, 
especially  in  the  oriental  countries  where  the  other  human  flukes 
abound  the  most.  Many  of  these  flukes  are  very  small,  but  they 
may  occur  in  great  numbers,  producing  practically  the  same  effects 
as  do  tapeworms,  —  anemia,  emaciation  and  general  debility. 
Many  species  are  probably  only  accidental  human  parasites, 
normally  living  in  some  other  host  but  occasionally  finding  their 
way  into  the  human  intestine  with  food  or  water  and  establishing 
themselves  there. 

The  smallest  fluke  parasitic  in  man  is  Yokagawa  (or  Metagonimus) 
yokagawa,  named  after  a  Japanese  parasitologist.  It  is  widely 
distributed  in  Japan,  Korea,  Formosa,  parts  of  China,  and  prob- 
ably other  oriental  countries.  It  infects  mice  and  dogs  as  well 
as  man.  Muto  infected  fish  with  the  encysted  cercerise  by  feed- 
ing to  them  cercaria-infected  snails,  Melania  Ubertina.  Encysted 
cercariae  occur  in  a  number  of  Japanese  fresh-water  fishes  which 
are  commonly  eaten  raw,  particularly  the  ''ayu".  The  cysts  are 
most  numerous  in  the  connective  tissue  under  the  skin  and  about 
the  fins,  especially  early  in  the  season,  indicating  that  the  fish 
become  infected  by  free-swimming  cercarise  which  bore  through 
the  skin,  and  not  by  cercarise  eaten  with  another  host.  The 
encysted  cercarise  closely  resemble  those  of  Clonorchis  sinensis. 
The  development  in  the  final  host  is  said  to  take  only  from  seven 
to  ten  days.  Y.  yokagawa  inhabits  the  upper  portion  of  the  small 
intestine,  sometimes  in  considerable  numbers,  but  it  never  seems 
to  do  enough  damage  to  cause  more  than  a  slight  intestinal  catarrh. 
It  is  remarkable  for  the  lack  of  a  ventral  sucker  and  is  only  about 
1  mm.  (about  ^V  of  an  inch)  in  length,  and  about  half  as  broad. 
Its  body  is  covered  with  a  great  many  microscopic  spines. 

A  very  similar  fluke,  Heterophyes  heterophyes  (Fig.  62),  only 
slightly  larger,  occurs  from  Egypt  to  Japan  in  a  variety  of 
animals  and  occasionally  parasitizes  man.     Two  species  of  Echi- 


INTESTINAL  FLUKES 


229 


nostoma  normally  parasitic  in  other  animals  occur  occasionally 
in  man  in  the  Malay  countries.  They  are  distinguished  from 
other  flukes  by  the  crown  of  spines  around  the  mouth  sucker. 
One  species,  E.  ilocanum,  about  one-fifth  of  an  inch  long,  was 
found  endemic  among  some  Filipinos  in  a  prison  in  Manila. 
The  other,  E.  malayanum,  about  two-fifths  of  an  inch  long,  oc- 
casionally parasitizes  man  in  the  Malay  countries. 

Gastrodiscoides  hominis  (Fig.  78)  is  a  species  which  is  character- 
ized by  the  expansion  of  the  posterior  end  of  the  body  into  a  great 


Fig.  78.  Gastrodicoides  hominis.  A,  ventral  view,  showing  disc-like  expansion 
and  posterior  position  of  ventral  sucker;  B  and  C,  dorsal  views;  D,  lateral  view; 
E,  eggs.     A-D,    X  3;   E,   X  65.     (After  Lewis  and  McConnell.) 

concave  disc.  It  is  a  small  reddish  brown  parasite  a  little  over 
one-fourth  of  an  inch  in  length,  which  inhabits  the  cecum  and 
large  intestine  of  hogs,  and  occasionally  of  man,  in  India.  A 
closely  allied  species  occurs  in  horses  and 
asses  in  many  parts  of  Africa.  Watsonius 
watsoni  (Fig.  79)  is  a  related  species,  also  l^^m^^^'^ 
reddish  brown  in  color,  found  in  the  small 
intestine  of  West  African  negroes.  A  closely 
related  species,  Paramphistomum  cervi,  is 
found  in  the  stomach  of  sheep  and  cattle  in 
Egypt  and  has  a  life  history  almost  identical 
with  that  of  the  sheep  liver  fluke.  This  or  a  Fig.  79.  Watsonius 
very  similar  species  occurs  in  the  stomach  of  ZnrgenZi^lper^rl 
cattle  in  the  United  States.  (gen.  ap.)   and  large 

Several  large  flukes  of  the  genus  Fasdolopsis  sJ^keAv!  s.).  x  about 
occur  occasionally  in  man,  especially  F.  buski  35.  (After  Shipley, 
(Fig.  80),  found  in  many  East  Asian  countries.  ^ZZ^^^'  ^""^  ^''^^' 
This  species  reaches  a  length  of  over  an  inch 
with  a  width  of  about  half  an  inch,  and  has  the  ventral  sucker 
very  close  to  the  mouth.  It  normally  inhabits  the  small  intestine 
of  the  hog  but  occasionally  parasitizes  man.  Goddard  found  it 
in  5.5  per  cent  of  all  dispensary  patients  at  Shaohing,  China, 
during  17  months,  and  in  28  per  cent  of  304  cases  admitted  to  the 


230 


THE  FLUKES 


hospital.  According  to  Goddard  there  are  three  stages  in  the 
disease  caused  by  this  parasite.  There  is  first  a  period  of  latency 
during  which  there  is  some  asthenia  and  mild  anemia.  This  is 
followed  by  a  period  of  diarrhea,  in  which  there  is  more  or  less 

intestinal  disorder;  there  is  however? 
no  blood  in  the  diarrheal  stools. 
There  is  always  noticeable  anemia, 
and  this  may  be  extreme.  A  com- 
bination of  chronic  diarrhea  and  an- 
emia is  said  to  be  characteristically 
the  result  of  Fasciolopsis  infection 
in  Shaohing.  Often  the  abdomen  is 
protuberant  in  children.  The  third 
stage  is  characterized  by  increased 
anemia  and  a  distressing  amount  of 
oedema,  which  affects  the  abdominal 
cavity  first,  then  the  legs,  and  finally 
the  upper  portions  of  the  body.  It 
gives  the  affected  parts  of  the  body  a 
very  characteristic  puffy  and  swollen 
appearance.  Goddard  believes  that 
the  infection  is  derived  from  eating 
imperfectly  cooked  snails,  some 
species  of  which  may  act  as  the  in- 
termediate host.  This  would  imply 
that  a  second  intermediate  host  was 
not  necessary  in  the  life  history. 
On  the  other  hand  it  has  been  claimed 
that  the  cercarise  encyst  in  shrimps, 
but  Leiper  had  no  success  in  infecting  hogs  with  the  cysts  which 
he  found  in  shrimps. 

The  full  life  history  of  none  of  these  intestinal  parasites  is 
known,  and  we  can  only  guess  at  them  by  analogy  with  more  or 
less  closely  related  parasites  about  which  we  have  more  knowledge. 
None  of  them  do  enough  damage  to  cause  more  than  slight  in- 
testinal irritation  or  catarrh,  and  sometimes  light  dysenteric 
symptoms.  They  are  susceptible  to  most  of  the  drugs  used  for 
expelling  tapeworms  and  roundworms.  Some  species  are  said 
not  to  be  affected  readily  by  santonin,  though  they  an?  ex- 
pelled by  thymol  and  naphthalene,  and  presumably  by  oil  of 
chenopodium. 


nat.dze. 
Fig.  80.       Fasciolopsishuski,     i 
large  intestinal  fluke  of  man.    x  2h 
Abbreviations  as  in  Fig.  74.       (Af 
ter  Odhner.) 


CHAPTER  XIII 


THE  TAPEWORMS 

General  Structure.  —  Even  more 
peculiar  and  remarkable  in  their 
structure  and  life  than  the  flukes 
are  the  tapeworms.  A  mature  tape- 
worm is  not  an  individual,  but  a 
whole  family,  consisting  sometimes 
of  many  hundreds  of  individuals  one 
behind  the  other  like  the  links  of  a 
chain  (Fig.  81).  In  some  respects 
the  tapeworms  are  more  degener- 
ate than  flukes,  due  to  their  in- 
variably parasitic  life  in  the  digestive 
tract  of  their  hosts.  Being  continu- 
ally bathed  in  semi-digested  fluids 
in  the  intestine  they  can  readily 
absorb  food  all  over  the  surface  of 
their  bodies,  and  have  no  need  for  a 
digestive  system  of  their  own.  The 
digestive  tract,  therefore,  is  entirely 
lacking,  not  even  a  vestige  of  it 
remaining  as  an  heirloom  from  less 
dependent  ancestors. 

In  general  form  the  majority  of 
tapeworms  are  very  long  tapelike 
organisms  which  attach  themselves 
to  their  host's  intestinal  walls  by  a 
"  head  "  or  scolex  at  what  is  really 
the   posterior  end   of   the   chain   of 

segments.      This    scolex    is    furnished        Fig.  81.     Beef  tapeworm,  Taenia 

with  suckers  and  often  hooks  as  well  gradTatchlnge  in°s*LTpmgiot- 

(Fig.    82).      Next    to   the  head    there    tids,  and  irregular  alternation  of 

ii         t    J)    sides  of  genital  apertures.     (After 

IS    a    narrow     region    or       neck      stiles.) 
which  continually  grows  and  forms 

segments  as  it  grows,  each  new  segment  thus  produced  pushing 
forward  the  segments  previously  formed.     This  process  eventu- 

231 


232 


THE  TAPEWORMS 


ally  produces  the  characteristic  chain  of  segments,  each  of  which 
is  known  as  a  proglottid.  Obviously  the  oldest  proglottid  is  the 
one  at  the  end  of  the  chain,  those  just  back  of  the  neck  being 

young  and  immature.  The  nervous 
system,  which  is  developed  into  a 
primitive  brainlike  mass  in  the  scolex, 
grows  forward  as  two  longitudinal 
nerves  which  run  continuously  through 
all  the  proglottids  in  the  chain.  The 
muscles  and  excretory  canals  also  run 
continuously  through  the  chain.  Each 
proglottid,  however,  possesses  com- 
plete reproductive  systems  of  both 
sexes,  fully  as  complex  as  in  the 
flukes,  if  not  more  so  (Fig.  83).  The 
female  system  consists  of  an  ovary,  a  pair  of  shell  glands  (usually 
spoken  of  as  yolk  glands),  a  seminal  receptacle  for  receiving  and 
holding  the  sperms  until  used  for  fertilization,  a  vagina  for  the 


un- 
or 


Fig.  82.  Armed  and 
armed  tapeworm  ' '  heads 
scoleces;  A,  unarmed  head  of 
ToBnia  saginata;  B,  armed  head 
of  Tcenia  solium.      X  10. 


gen.f. 


Fig,  83.  Sexually  mature  proglottid  of  beef  tapeworm,  Tcema  sa^mato;  exec, 
excretory  canal;  n.,  nerve  cord;  ut.,  uterus;  ov.,  ovary;  sh.  gl.,  shell  gland, 
usually  called  yolk  gland;  vag.,  vagina;  gen.  p.,  genital  pore;  sp.  d.,  sperm  duct; 
t.,  testis.     X  7.     (Partly  after  Leuckart.) 

entrance  of  the  sperms,  and  a  uterus  for  the  storage  of  the  mature 
fertilized  eggs.  The  male  system  consists  of  a  number  of  scat- 
tered testes  for  production  of  sperms,  all  connecting  by  minute 
tubes  with  the  sperm  duct.  The  latter,  near  where  it  opens  at 
the  surface  of  the  body,  enlarges  into  a  ''  cirrus  pouch  "  where 


REPRODUCTION 


233 


the  mature  sperms  are  temporarily  stored.  The  sperm  duct 
ends  in  an  extensible  copulatory  organ  for  conducting  the  sperms 
into  the  vagina  of  the  same  or  another  proglottid.  Though 
hermaphroditic,  i.e.,  with  both  sexes  in  a  single  individual,  a 


Fig.  84.  Ripe  proglottids  of  various  tapeworms  of  man,  drawn  to  scale  accord- 
ing to  average  measurements:  A,  Toenia  saginata  (after  Leuckart).  B,  Tcenia  solium 
(after  Stiles).  C,  Dipylidium  caninum  (after  Diamare).  D,  Tcenia  confusa  (after 
Guyer).  E,  Dibothriocephalus  latus  (after  Leuckart).  F,  Diplogonoporus  grandis 
(after  Ijima  and  Kurimoto).  G,  Dibothriocephalus  cordatus  (after  Leuckart).  H, 
Tcenia  africana  (after  von  Linstow).  /,  Hymenolepis  diminuta  (after  Grassi). 
/,  Hymenolepis  nana  (after  Leuckart). 

proglottid  does  not  necessarily  always  fertilize  its  own  eggs, 
but  cross-fertilization  may  often  occur.  This  is  generally  in- 
sured by  the  fact  that  the  male  reproductive  system  usually 
becomes   mature  before   the  female.     In  the  pork  tapeworm, 


234  THE  TAPEWORMS 

for  instance,  the  male  reproductive  system  reaches  maturity 
when  the  proglottid  has  been  pushed  back  to  about  the  200th 
position,  whereas  the  female  system  does  not  mature  until  it 
has  been  pushed  200  or  300  proglottids  farther  back.  Copulation 
then  takes  place  by  the  doubhng  back  of  the  chain  of  proglottids 
on  itself,  bringing  the  young  mature  male  segments  into  contact 
with  the  older  mature  female  segments. 

After  copulation,  when  the  mature  fertilized  eggs  begin  to  form, 
great  changes  take  place  in  the  proglottid.  The  uterus  begins 
to  enlarge  and  branch  until  it  nearly  fills  the  segment,  crowding 
aside  and  absorbing  the  other  organs.  Segments  thus  distended 
with  eggs  are  spoken  of  as  ''  ripe  "  proglottids  and  are  ready  to 
break  loose  from  the  chain  to  be  voided  with  the  faeces  of  the  host. 
Ripe  proglottids  of  a  number  of  species  of  tapeworms  found  in 
man  are  shown  in  Fig.  84. 

Life  History.  —  The  life  histories  of  all  tapeworms  are  much 
alike.     Usually  before  the  ripe  proglottids  become  detached  and 

pass  out  of  the  host,  the 
eggs  develop,  inside  their 
tough  shell,  into  little 
round  embryos  with  six 
hooks  (Fig.  85 A).  In 
order  to  continue  their 

Fig.  85.     A,  egg  of  beef  tapeworm,  T.  saginata;  ^        i  +  V. 

—  note  contained  embryo  and  external  filaments;  development     SUCn     em- 

B,  freed  six-hooked  embryo.  X  300.  (After  bryOS  mUSt  be  eaten  by 
Leuckart.)  ,i  •         <•        •        i 

another  species  of  animal 
which  acts  as  an  intermediate  host.  Most  often  the  adult 
form  of  the  worm  occurs  in  carnivorous  animals,  while  the  in- 
termediate host  in  which  the  larva  develops  is  a  herbivorous 
animal,  but  there  are  numerous  exceptions  to  this.  There  is  no 
active  search  for  a  new  host  on  the  part  of  the  tapeworm  embryo 
as  there  is  by  the  embryos  of  flukes,  but  instead  merely  a 
passive  transfer. 

When  eaten  by  a  suitable  intermediate  host,  the  shell  enclosing 
the  six-hooked  embryo  is  dissolved  off,  and  the  embryo  is  re- 
leased (Fig.  85B).  It  migrates  into  the  organs  and  tissues  of 
the  body,  aided  by  the  blood  and  lymph  circulation  of  the  host, 
some  species  having  preference  for  certain  organs,  others  es- 
tablishing themselves  with  equal  readiness  in  any  parts  which 
they  happen  to  reach. 


TYPES  OF  TAPEWORM  LARV^ 


235 


Having  reached  the  organ  or  tissue  in  which  it  is  destined  to 
develop,  the  embryo  loses  its  hooks  and  grows  into  some  form  of 
bladderworm,  that  is,  the  body  undergoes  a  series  of  transfor- 
mations which  usually  result  in  the  formation  of  a  bladder-like 
body  filled  with  a  watery  fluid.  Into  the  bladder  there  grows 
an  invagination  and  at  the  bottom  of  this,  pushed  inside  out  into 
it,  there  develops  a  head  or  scolex.  There  are  different  types 
of  bladderworms  which  go  under   different  names,  as  follows: 

(1)  the  cysticercus  (Fig.  86 A),  the  simple  type  described  above; 

(2)  the  cysticercoid  (Fig.  86B),  in  which  the  bladder  part  of  the 


Fig.  86.  Types  of  tapeworm  larvae:  A,  cysticercus  of  Toenia  solium  with  head 
and  neck  evaginated,  X  3;  B,  cysticercoid  of  Hymenolejns  nana,  X  12;  C,  plerocer- 
coid  of  Dibothriocephalus  latus,  with  head  invaginated.  (A,  partly  after  Stiles,  B, 
from  several  figs,  by  Grassi  and  Rovelli;    C,  partly  after  Braun.) 


worm  is  poorly  developed;  (3)  the  coenurus,  in  which  multiple 
heads  form  in  the  single  bladder;  and  (4)  the  hydatid,  in  which 
the  bladder  buds  into  multiple  daughter  cysts,  each  with  multiple 
heads  (Fig.  95).  The  larvae  of  the  tapeworms  of  the  family 
Dibothriocephalidce  are  quite  unlike  the  bladderworms  of  other 
tapeworms.  They  grow  as  long  wrinkled  wormlike  bodies  with 
the  head  invaginated  in  a  little  projection  at  the  anterior  end. 
Such  a  larva  is  called  a  plerocercoid  (Fig.  86C). 

When  the  organs  or  tissues  in  which  the  larval  stages  are 
developed  are  eaten  by  an  animal  of  the  kind  from  which  the  eggs 
originally  came,  all  but  the  scolex  of  the  bladderworm  is  digested 
off,  the  latter  turns  right  side  out,  attaches  itself  to  the  wall  of 
the  small  intestine  with  the  aid  of  its  suckers  and  hooks,  and  be- 
gins to  bud  off  proglottids  of  another  generation.  Tapeworms 
are  usually  looked  upon  as  inert  animals,  but  in  reality  they  are 
quite  active,  and  their  movements  can  often  be  felt. 


236  THE  TAPEWORMS 

Damage  to  Host.  —  The  amount  of  damage  which  adult 
tapeworms  do  to  their  hosts  is  a  much  disputed  question.  There 
are  those  who  beheve  that  the  presence  of  an  adult  tapeworm  is 
more  or  less  of  a  joke  and  as  such  is  to  be  gotten  out  of  the  sys- 
tem but  not  to  be  taken  seriously.  The  experience  of  physicians 
who  have  had  wide  dealings  with  tapeworms  does  not  ordinarily 
bear  out  this  idea.  The  mere  mechanical  obstruction  of  the 
intestine  which  a  large  tapeworm  may  cause  must  be  consider- 
able. The  amount  of  food  taken  from  the  host  for  nourishment 
of  such  a  worm  might  well  be  compared  with  the  food  absorbed 
by  a  growing  embryo,  and  it  usually  produces  a  ravenous  appetite. 
The  injury  to  the  wall  of  the  intestine  caused  by  the  adhesion 
of  the  worm  by  its  suckers  and  hooks  is  often  the  cause  of  serious 
conditions,  allowing  the  entrance  of  bacteria  and  sometimes 
resulting  in  destructive  ulceration.  The  waste  products  and 
other  toxic  substances  given  off  by  tapeworms  must  be  very  con- 
siderable and  their  poisonous  properties  cannot  be  doubted. 
Only  recently  there  came  before  the  notice  of  the  author  a  case 
of  tapeworm  infection  illustrating  the  toxic  effect  of  the  worms. 
A  patient  came  to  a  local  physician  for  treatment,  thinking  he 
had  tuberculosis  and  having  been  so  diagnosed  by  another  doc- 
tor. He  was  in  an  extremely  anemic  condition  and  was  very 
weak  and  easily  exhausted.  His  cheeks  were  sunken,  his  eye 
staring  and  he  was  subject  to  occasional  mental  disturbances. 
Within  a  fortnight  after  the  worm  had  been  expelled  he  was  prac- 
tically a  new  man  although  he  had  been  suffering  for  over  a  year. 

Abdominal  pains,  anal  itching,  disordered  appetite  and  di- 
gestion, emaciation,  anemia  and  many  types  of  nervous  derange- 
ments, as  giddiness,  partial  paralysis,  false  sensations  and  epilep- 
tic fits,  are  common  symptoms  of  tapeworm  infection.  The 
degree  to  which  each  of  these  symptoms  is  felt  varies  remarkably 
in  different  individuals.  The  nervous  symptoms  are  all  due  to 
intoxicating  substances  liberated  by  the  worms.  Sometimes 
a  partial  immunity  to  the  toxic  effects  of  worms  is  acquired  by 
infected  people,  and  in  such  cases  the  worms  may  be  present 
unnoticed  for  years. 

The  damage  done  by  bladderworm  stages  of  tapeworms  is 
often  more  serious,  especially  in  the  case  of  hydatids,  the  large 
multiple  bladderworms  of  Echinococcus  granulosus.  The  bladder- 
worms  which  occur  in  man  most  commonly  develop  in  the  lung 


TREATMENT  AND  PREVENTION  237 

or  liver,  but  may  attack  other  parts  of  the  body  such  as  the 
muscles,  eye  and  even  the  brain.  They  do  injury  both  by  me- 
chanical interference  with  the  organs  and  tissues,  and  by  the 
accumulation  of  poisonous  waste  products  which  may  be  ac- 
cidentally liberated.  Only  by  surgery  can  such  bladderworms 
be  removed,  and  surgery  is  often  impossible  on  account  of  the 
numbers  and  positions  of  the  bladders. 

Treatment.  —  Preparatory  to  treatment  for  adult  tapeworm  in- 
fections the  patient  is  put  on  a  light  diet  and  his  bowels  cleared  out 
so  that  the  parasite  may  meet  with  no  obstruction  in  its  passage 
through  the  intestine.  The  drugs  which  have  been  found  most 
useful  in  expelling  tapeworms  are  male  fern,  pelletririne  and 
thymol.  These  drugs  are  dangerous  if  not  taken  properly,  and 
none  should  be  taken  without  the  supervision  of  a  physician. 
Thymol,  for  instance,  while  ordinarily  quite  harmless  since  it  is 
not  absorbed  by  the  intestine,  is  soluble  in  alcohol  and  certain  other 
substances  and  may  cause  death  if  taken  along  with  these  things. 
Oil  of  chenopodium,  which  has  recently  come  into  great  favor 
for  expelling  hookworms  and  is  even  more  efficient  for  certain 
other  nematodes,  has  been  found  valuable  for  expelling  dwarf 
tapeworms,  Hymenolepis  nana,  and  would  probably  be  equally 
effective  for  other  species. 

After  the  drug  is  administered  a  purgative  is  given  which  tends 
to  drive  the  parasite  out.  The  latter  should  be  passed  into  a 
vessel  of  warm  water,  since  sudden  contact  with  cold  stimulates 
the  nervous  system  of  the  worm  and  causes  it  to  contract  sud- 
denly, thus  often  breaking  it  before  it  has  been  completely  ex- 
pelled. A  careful  search  for  the  head  should  be  made,  and  if 
not  found  the  treatment  should  be  repeated  in  the  course  of  a 
week  or  ten  days. 

Prevention.  —  Prevention  varies,  of  course,  with  the  species  of 
tapeworm  and  its  intermediate  host,  but  since  infection  with  all 
the  common  human  species,  with  the  exception  of  the  species 
of  Hymenolepis,  occurs  from  eating  raw  or  imperfectly  cooked 
meat  of  some  kind  in  which  the  bladderworms  have  devel- 
oped, the  exclusive  use  of  thoroughly  cooked  meat  is  the  best 
preventive  measure.  Experiments  show  that  pork  bladder- 
worms  are  killed  when  heated  to  127°  F.  and  beef  bladderworms 
to  120°  or  even  less,  but  the  difficulty  of  heating  the  center  of  a 
large  piece  of  meat  even  to  this  point  is  shown  by  the  fact  that 


238 


THE  TAPEWORMS 


in  an  experiment  to  test  the  penetration  of  heat,  a  ham  cooked 
by  boiUng  for  two  hours  had  reached  a  temperature  of  only 
115°  in  the  center.  When  roasted,  pork  should  always  be  cut 
into  pieces  weighing  no  more  than  three  or  four  pounds  to  insure 
thorough  penetration  of  heat.  Beef  which  has  lost  its  red  or 
"  rare  "  color  is  quite  safe. 

Since  bladderworms  are  unable  to  survive  the  death  of  their 
host  for  more  than  a  limited  time,  they  are  eventually  destroyed 
by  ordinary  cold  storage  —  within  three  weeks  in  the  case  of  the 
beef  bladderworm,  Cysticercus  hovis,  but  not  always  so  soon  in 
the  case  of  the  pork  bladderworm,  C.  cellulosce.  According  to 
Dr.  Ransom  temperatures  of  about  15°  F.  kill  beef  bladder- 
worms  within  five  days.  Thorough  curing  or  salting  of  meat  is 
also  destructive  to  the  parasites. 

Infected  persons  should  be  careful  not  to  contaminate  the 
food  or  water  of  domestic  animals  with  their  faeces,  bearing  in 


Fig.  87.  Heads  of  some  adult  tapeworms  found  in  man,  drawn  to  scale;  A, 
beef  tapeworm,  Tcenia  saginata;  B,  pork  tapeworm,  T.  solium;  C,  fish  tapeworm, 
Dibothriocephalus  latus;  D,  heart-headed  tapeworm,  Dibothriocephalus  cordatus; 
E,  African  tapeworm,  T.  africana;  F,  double-pored  dog  tapeworm,  Dipylidium 
caninum;  G,  dwarf  tapeworm,  Hymenolepis  nana;  H,  rat  tapeworm,  Hymenolepis 
diminuta.      X  10. 

mind  the  various  ways  in  which  the  eggs  may  be  disseminated 
—  by  streams,  rain,  flies,  etc. 

The  eggs  of  the  dwarf  tapeworm,  Hymenolepis  nana,  are 
thought  to  be  able  to  develop  through  the  bladderworm  stage 
to  the  adult  in  a  single  host,  and  should  therefore  be  guarded 
against  by  different  measures  (see  p.  243).  The  larvae  of  other 
species  of  Hymenolepis  develop  in  insect  larvae  such  as  mealworms, 
and  are  therefore  subject  to  still  different  means  of  prevention. 

The  tapeworms  of  man  belong  to  two  quite  distinct  families, 
the  Taeniidae,  in  which  the  scolex  is  rounded  and  furnished  with 
four  cup-shaped  suckers  (Fig.  87,  A,  B,  E,  F,  G  and  H),  and  the 


BEEF  TAPEWORM 


239 


Dibothriocephalidse,  in  which  the  head  is  flat  and  possesses  two 
sUthke  suckers  (Fig.  87C  and  D).  The  latter  family  also  differs 
from  the  Taeniidse  in  having  eggs  with  lids  like  those  of  the 
flukes  (Fig.  88 A),  and  without  developed  embryos  when  passed 
in  the  faeces. 


The 


Family  Taeniidae 

Beef  Tapeworm.  —  The  commonest  human  tapeworm  in  most 
parts  of  the  world  is  the  beef  tapeworm,  Tcenia  saginata. 
adult  of  this  species  as  it  occurs  in  the 
human  small  intestine  consists  of  over 
1000  proglottids,  and  grows  to  a  length  of 
15  or  20  feet;  cases  have  been  reported 
of  specimens  of  this  tapeworm  which 
measured  35  to  40  feet,  though  in  some 
of  these  cases  there  were  probably  several 
tapeworms  infesting  a  single  person. 
When  two  or  more  worms  are  expelled 
in  pieces  it  would  naturally  be  easy  to 
measure  them  as  parts  of  a  single  one. 

The  scolex  of  the  beef  tapeworm  (Fig. 
82 A)  is  hardly  larger  than  the  head  of  a 
pin.  It  possesses  four  small  suckers  for 
adhering  to  the  wall  of  the  intestine,  but 
there  is  no  crown  of  hooks.  The  suckers 
are  apparently  quite  sufficient  for  main- 
taining a  hold,  if  one  should  judge  from 
the  difficulty  experienced  in  dislodging  the 
worm  from  the  intestine. 

The  proglottids  gradually  increase  in 
size  as  they  get  farther  from  the  scolex  (Fig.  81),  and  the  organs 
contained  in  them  develop  slowly.  The  general  form  of  a  sexu- 
ally mature  proglottid  and  the  appearance  and  arrangements  of 
the  organs  are  shown  in  Fig.  83.  Shortly  after  sexual  maturity  has 
been  reached  and  the  sperms  for  fertilizing  the  eggs  have  been 
received,  the  uterus  begins  to  grow  and  develop  lateral  branches 
to  accommodate  the  rapidly  forming  eggs.  When  fully  developed 
the  gravid  proglottid  enlarges,  becoming  three  or  four  times  as 
long  as  when  sexually  mature,  and  resembles  a  pumpkin  seed 
in  shape.     The  greatly  developed  uterus,  distended  with  eggs, 


Fig.  88.  Gravid  segment 
of  Tcenia  saginata.  X  4. 
(After  Stiles.) 


240  THE  TAPEWORMS 

occupies  practically  the  whole  segment,  while  nearly  all  the  other 
organs  degenerate  (Fig.  88). 

A  man  infested  by  a  beef  tapeworm  expels  several  hundred 
proglottids  a  month,  each  one  gorged  with  many  thousands  of 
eggs.  Fortunately  the  majority  of  these  never  get  an  opportunity 
to  develop  further  but  it  is  easy  to  see  how  some  of  the  eggs  may 
reach  their  intermediate  hosts,  cattle,  if  the  people  who  harbor 
the  worms  are  at  all  careless.  Disseminated  by  rain  water, 
washed  by  streams  into  drinking  troughs,  carried  about  on  the 
feet  of  flies,  adhering  to  the  heel  of  a  boot,  and  in  many  other 
ways  the  eggs  passed  with  the  faeces  may  be  transferred  to  the 
grass  or  water  eaten  by  cattle.  In  India,  where  this  tapeworm 
is  common,  cattle  are  said  to  devour  human  excrement  if  they 
have  access  to  it. 

When  eaten  by  cattle  or  other  ungulates,  as  the  pronghorn 
antelope,  giraffe  and  llamas,  the  six-hooked  embryos  (Fig.  85) 
escape  from  the  eggs  and  migrate  into  the  muscles  of  the  new 
host,  attacking  especially  the  muscles  of  mastication.  Here  in  the 
course  of  from  three  to  six  weeks  they  grow  into  bladderworms, 
Cysticercus  hovis,  about  one-third  of  an  inch  in  length.  They  are 
grayish  white  in  color  with  a  little  yellow  spot  where  the  head  is 
invaginated.  The  fact  that  the  cysts  lack  any  marked  contrast 
to  the  muscle  tissue,  and  if  not  very  numerous  may  be  obscured 
by  it,  causes  them  to  be  overlooked  frequently.  If  present  they 
can  usually  be  found  most  readily  in  the  muscles  of  mastication 
or  in  the  heart;  these  are  the  portions  of  the  carcass  regularly 
examined  in  meat  inspection.  Beef  which  contains  bladder- 
worms  is  said  to  be  "  measly." 

Infection  of  man  results,  of  course,  from  eating  measly  beef 
which  is  raw  or  only  partially  cooked.  In  Abyssinia  the  Moham- 
medans, who  are  forbidden  by  rehgious  law  to  eat  raw  meat,  are 
practically  free  from  tapeworm  infection,  whereas  practically 
all  the  non-Mohammedans  are  infected.  The  ripe  proglottids 
begin  to  appear  in  the  faeces,  several  at  a  time,  in  the  course  of 
two  or  three  months  after  infection,  and  may  continue  to  be 
developed  for  years. 

Pork  Tapeworm.  —  Common  in  some  parts  of  the  world,  but 
very  rare  in  the  United  States,  is  the  species  Tcenia  solium, 
which  passes  its  bladderworm  stage  in  hogs.  Wherever  raw  or 
imperfectly  cooked  pork  is  eaten,  infection  with  this  tapeworm  is 


PORK  TAPEWORM 


241 


likely  to  occur.  The  infrequence  of  these  tapeworms  in  the 
Philippines  where  the  bladderworms  are  very  common  in  hogs 
is  worthy  of  note. 

The  adult  Tcenia  solium  differs  from  the  beef  tapeworm  chiefly 
in  the  form  of  the  scolex,  which  in  addition  to  four  suckers  is 
armed  with  a  double  row  of  hooks,  arranged  on  a  conical  pro- 
jection or  "  rostellum  "  at  its  apex  (Fig.  82B).  The  worms  are 
usually  of  less  length  than  beef  tapeworms,  seldom  exceeding 
from  six  to  ten  feet;  they  consist  of  about  800  or  900  segments. 
The  ripe  proglottids  (Fig.  84B)  can  in  most  cases  be  distinguished 
from  those  of  the  beef  tapeworm  by  their  ufiually  smaller  size 
and  fewer  branches  of  the  uterus  (compare  Figs.  84A  and  B). 

The  eggs,  passed  in  the  ripe  proglottids  with  the  faeces,  develop 
into  bladderworms  when  eaten  by  hogs  or  cer- 
tain other  animals.  The  usual  filthy  way  in 
which  hogs  are  housed  and  fed  gives  ample 
opportunity  for  infection  if  the  infested  people 
are  at  all  careless  in  their  personal  habits,  or 
if  privies  are  built  so  that  they  leak  and  the 
hogs  have  access  to  the  surrounding  ground  or 
outflowing  streams.  Young  pigs  are  especially 
hkely  to  become  ''  measly  "  from  eating  tape- 
worm eggs. 

As  soon  as  the  eggs  reach  the  intestine 
the  six-hooked  embryos  are  liberated  from  of  measly  pork.  (After 
the  enclosing  capsule  and  make  their  way 
through  the  wall  of  the  intestine,  to  be  carried  by  bloodvessels 
to  the  place  where  they  are  to  develop.  They  may  develop 
in  almost  any  or  all  of  the  muscles  or  organs  of  the  hog's  body, 
but  they  especially  favor  the  tongue,  neck  and  shoulder  muscles, 
and,  next  in  order,  certain  muscles  of  the  hams.  Sometimes 
the  bladderworms,  technically  known  as  Cysticercus  cellulosce,  be- 
come so  numerous  as  to  occupy  over  one-half  of  the  total  volume 
of  a  piece  of  flesh  examined,  i.e.,  several  thousand  to  a  pound. 
They  appear  as  small  elliptical  bladders  from  6  to  18  mm.  (one- 
fourth  to  three-fourths  of  an  inch)  in  length  (Fig.  89).  They 
have  a  whitish  spot  at  about  the  middle  of  the  length,  in  the  center 
of  which  is  the  opening  where  the  head  is  invaginated. 

Unlike  the  beef  tapeworm,  Tcenia  solium  can  pass  its  bladder- 
worm  stage  in  a  number  of  animals,  namely  hogs,  man  and  dogs. 


Fig.  89.     Fragment 


242  THE  TAPEWORMS 

They  have  been  reported  in  a  considerable  number  of  other 
animals  also  but  the  cases  are  very  doubtful.  The  fact  that  the 
larval  stage  can  develop  in  man  makes  the  species  particularly 
dangerous  on  account  of  possibility  of  self-infection,  either  by 
contaminated  hands  or  by  a  reversal  of  the  peristaltic  movements 
of  the  intestine  which  throws  the  ripe  proglottids  of  the  worm  back 
into  the  stomach  where  the  embryos  in  the  eggs  are  liberated  by 
the  gastric  juices.     This  is  discussed  further  on  p.  251. 

The  Dwarf  Tapeworms.  —  The  dwarf  tapeworm,  Hymenolepis 
nana  (Fig.  90A),  is  the  smallest  tapeworm  found  in  man,  but 

it  often  occurs  in  such  numbers  as  to 
cause  much  irritation  in  the  intestine. 
It  is  a  common  parasite  in  Italy,  and 
occurs  throughout  the  warm  parts  of 
Europe,  Asia,  Africa  and  America.  It 
is  probably  much  more  common  in  the 
United  States  than  is  generally  sup- 
posed, since  it  can  easily  be  overlooked 
unless  the  faeces  are  microscopically 
examined  for  eggs.  It  is  probably  a 
common  parasite  of  rats  and  mice  as 
well  as  of  man,  though  the  rodent  par- 
FiG.  90.  A,  dwarf  tapeworm,  ^site  is  believed  by  some  parasitolo- 
Hymenoiepis  nana,  X  7  (after  gists  to  be  a  distinct  species,i?.m2^nna. 
Wter  kfi^m)"' "' """"'  ""  '"^   Utiles  considers  the  rodent  parasite  a 

sub-species,  H.  nana  fraterna. 
The  adult  worm,  which  consists  of  from  100  to  200  proglottids, 
is  usually  little  over  an  inch  in  length  and  less  than  one  mm.  (-^ 
of  an  inch)  in  width.  The  scolex  (Fig.  87G)  has  four  tiny  suckers 
and  a  crown  of  little  hooks.  The  ripe  proglottids  (Fig.  84J) 
differ  from  those  of  the  large  tapeworms  in  being  much  wider 
than  long,  with  the  enlarged  uterus  in  the  form  of  a  solid  mass, 
partially  divided  into  compartments  instead  of  being  branched. 
As  regards  life  history,  the  dwarf  tapeworm  is  commonly  be- 
lieved to  pass  both  its  larval  and  adult  stages  in  a  single  host, 
contrary  to  what  occurs,  so  far  as  is  known,  in  any  other  tape- 
worm. The  eggs  (Fig.  90B),  eaten  by  a  rat  or  man,  liberate  six- 
hooked  embryos  in  the  small  intestine,  where  they  enter  the  villi 
and  transform  into  cysticercoid  bladderworms  (Fig.  86B),  which 
in  turn  fall  into  the  cavity  of  the  intestine,  attach  themselves 


DWARF  TAPEWORM 


243 


by  the  armed  head,  and  become  adult.  It  is  said  that  eggs  of 
this  parasite  can  be  found  in  the  faeces  within  a  month  after  an 
egg  of  the  preceding  generation  has  been  swallowed.  Self- 
infection  with  these  eggs  rarely  occurs,  since  the  eggs  will  not 
develop  unless  acted  upon  by  the  gastric  juices.  There  is  still 
room  for  doubt  as  to  whether  an  insect  is  not  commonly  involved 
as  an  intermediate  host  as  in  other  species  of  Hymenolepis;  in 
fact,  several  investigators  have  found  cysticercoids  in  rat  fleas 
which  they  ascribed  to  this 
species.  Ransom  thinks 
there  is  room  for  doubt 
as  to  whether  the  larvae  of 
Hymenolepis  found  in  the 
intestinal  villi  of  rats  and 
mice  break  out  and  become 
mature  in  the  lumen. 

The  common  presence 
of  this  parasite  or  a  variety 
of  it  in  rats  and  mice  indi- 
cates that  infection  in  man 
may  occur  from  accident- 
ally swallowing  the  '^  pills  " 
of  these  animals  infected 
with  the  eggs  or  ripe  pro- 
glottids  of  the  worm. 
Since  a  single  mouse  "  pill " 
might  contain  hundreds 
of  eggs,  each  of  which 
could  develop  into  an 
adult  in  another  rat  or 
mouse,  or  in  man,  it  is 
not  difficult  to  understand  the  great  numbers  of  this  worm  which 
are  often  found  in  a  single  intestine. 

The  unique  life  history  of  this  species,  if  true,  makes  it  subject 
to  entirely  different  preventive  measures  from  those  used  against 
most  other  tapeworms.  Since  infection  results  not  from  eating 
bladderworm-infected  meat,  but  probably  from  swallowing  egg- 
infected  faeces,  especially  the  "  pills  "  of  mice  and  rats,  and  pos- 
sibly also  from  swallowing  infected  insects  which  are  acting  as 
intermediate  hosts,   prevention  consists  in  the  elimination  of 


Fig.  91. 
nuta,  from 
size. 


Rat  tapeworm,  Hymenolepis  dimi- 
house  mouse  in   Oregon.     Natural 


244 


THE  TAPEWORMS 


rats  and  mice  from  the  household  and  in  keeping  food  out  of 
their  reach,  and  in  guarding  against  the  accidental  ingestion  of 
such  possible  intermediate  hosts  as  fleas. 

A  closely  allied  species,  H.  diminuta  (Fig.  91),  occurs  rarely 
in  man.  It  closely  resembles  the  dwarf  tapeworm  but  is  of 
larger  size  (four  to  24  inches  in  length)  and  has  no  hooks  on  the 
scolex  (Fig.  87H).  The  eggs  develop  in  the  larvae  or  adults  of 
the  mealworm,  Asopia  farinalis,  and  in  other  insects,  forming 
cysticercoids.  When  these  are  eaten  by  rats,  mice  or  man  they 
transform  into  adults.  In  an  experiment  on  man  the  eggs  of 
the  adult  worm  were  found  in  the  faeces  15  days  after  the  eating 
of  an  infected  mealworm.  The  larvae  of  a  number  of  species 
of  fleas  also  become  infected  when  they  ingest  the  eggs.  It  is 
evident  that  prevention  consists  in  guarding  carefully  against 
the  accidental  swallowing  of  mealworms  with  cereals  or  other 
foods,  and  in  cautioning  children  against  putting  beetles  or 
other  insects  into  their  mouths.  Although 
the  worm  is  rare  in  man  it  is  common  in 
rats  and  mice  in  many  parts  of  the  world, 
and  occurs  in  nearly  all  parts  of  the  United 
States. 

Other  Tapeworms  (Taeniidae).  —  A  con- 
siderable number  of  other  tapeworms  of  this 
family  have  been  found  in  man,  acciden- 
tally occurring  in  him,  or  having  a  very 
hmited  distribution. 

Of  those  with  limited  distribution  should 
be  mentioned  two  species  of  Davainea.  One, 
D.  madagascariensis  (Fig.  92),  is  a  small 
tapeworm  reaching  a  length  of  ten  or  twelve 
inches.  It  is  found,  chiefly  in  children,  in  many  tropical  countries, 
especially. in  islands  and  seaports  and  on  ships.  The  suggestion  has 
been  offered  that  the  intermediate  host,  so  far  unknown,  may  be 
the  ubiquitous  sea-going  cockroach.  This  tapeworm  is  interesting 
in  that  there  is  not  only  a  crown  of  hooks  on  the  head,  but  there 
are  hooks  on  the  suckers  also.  The  other  species  of  Davainea 
is  D.  formosana,  recently  described  by  Akashi  from  children  in 
Formosa  and  Tokyo.  It  differs  from  the  preceding  species  in 
its  larger  size,  lack  of  hooks  on  the  suckers,  larger  size  of  egg 
masses  in  the  ripe  proglottids  and  in  other  minor  details. 


Fig,  92.  Davainea  mad- 
a^a^cariensis;  A,  head  and 
neck,  B,  gravid  proglottids. 
X  8.  (A,  after  Blanchard, 
B,  after  Daniels.) 


DIBOTHRIOCEPHALIDiE  245 

The  African  tapeworm,  Tcenia  africana,  is  a  species  found  in 
German  East  Africa.  It  is  about  four  feet  in  length  with  no 
hooks  on  the  scolex  (Fig.  87E)  and  with  an  unusual  fanUke  ar- 
rangement of  the  uterus  in  the  ripe  proglottids  (Fig.  84G).  Von 
Linstow,  who  described  the  worm,  suggests  that  the  zebu  may 
be  the  intermediate  host  since  its  flesh  is  eaten  raw  by  the 
natives. 

A  medium-sized  tapeworm,  TcBuia  philippina,  reaching  a 
length  of  about  three  feet,  has  been  found  among  prisoners  at 
Manila.  It  very  much  resembles  the  African  tapeworm  but  has 
smaller  proglottids.  Other  species  have  been  described  from 
various  parts  of  the  world,  especially  southern  Asiatic  Russia, 
but  they  are  of  such  rare  occurrence,  some  having  been  found 
only  once,  that  they  need  no  description  here. 

Two  specimens  of  the  species  Taenia  confusa  (Fig.  84D,)  were 
found  by  Ward  in  Nebraska  many  years  ago,  and  recently  another 
specimen  was  reported  by  Chandler  from  Texas.  It  probably  has 
been  endemic  in  the  central  states  in  the  meantime,  but  confused 
with  other  species.  It  is  possibly  identical  with  T.  hremneri  of 
Africa. 

Of  the  accidental  tapeworms  of  man  there  should  be  mentioned 
especially  the  dog  tapeworm,  Dipylidium  caninum.  This  species 
is  abundant  in  dogs,  and  sometimes  cats,  in  all  parts  of  the 
world.  It  is  a  species  about  a  foot  in  length,  with  three  or  four 
rows  of  hooks  on  the  rostellum  (Fig.  87F),  and  a  double  set  of 
reproductive  organs  in  each  proglottid  (Fig.  84C).  The  larva, 
a  cysticercoid,  occurs  in  lice  and  fleas.  It  is  stated  that  the  eggs 
of  this  tapeworm  cannot  be  sucked  up  by  the  dog-infesting  fleas, 
but  that  they  are  readily  swallowed  by  flea  larvae.  The  eggs  hatch 
in  the  intestine  of  the  flea  larvae,  the  embryos  pass  to  the  body 
cavity  and  the  cysticercoids  remain  through  the  metamorphosis 
of  the  larvae  to  the  adult  fleas.  Children  who  play  with  dogs 
are  occasionally  infested  by  this  worm,  probably  by  accidentally 
swallowing  lice  or  fleas  or  by  crushing  them  and  then  putting  in- 
fected fingers  into  the  mouth. 


Family  Dibothriocephalidae 

The  tapeworms  of  this  family,  as  remarked  before,  are  charac- 
terized by  a  flattened  head  with  two  slitlike  suckers  (Fig.  87C 
and  D).     The  larvae,  which  usually  develop  in  fishes,  are  of  the 


246 


THE  TAPEWORMS 


plerocercoid  type,  i.e.,  they  have  long  wormlike  bodies  with  an 
invaginated  head  at  one  end  (Fig.  86C). 

Fish  Tapeworm.  The  common  fish  tapeworm  of  man, 
Diphyllobothrium  latus,  is  an  important  species  in  the  districts 
in  which  it  occurs.  It  is  found  in  all  countries  where  fresh- water 
fish  is  extensively  eaten,  and  especially  in  countries  where  it  is 
commonly  eaten  raw.  In  the  Baltic  countries,  Switzerland, 
Russia,  Japan,  and  about  the  Central  African  lakes  this  parasite 
is  particularly  common.  Relatively  few  cases  have  been  re- 
ported in  the  United  States,  though  the  larvae  are  said  to  be  found 
frequently  in  fish  from  the  Great  Lakes. 

The  fish  tapeworm  is  a  large  species  and  commonly  reaches  a 
length  of  from  six  to  30  feet,  or  even  more, 
with  from  2000  to  4200  short,  broad  pro- 
glottids,  only  the  terminal  ones  of  which 
are  as  long  as  broad.  The  scolex  (Fig.  87C) 
is  almond-shaped.  Unlike  the  tapeworms 
of  the  family  Tseniidse,  the  genital  openings 
are  near  the  middle  of  the  under  surface  of 
the  proglottids,  instead  of  at  one  side.  In 
the  ripe  proglottids  (Fig.  84E)  the  uterus 
is  in  the  form  of  a  rosette  near  the  center 
of  the  segment.  The  proglottids  do  not 
usually  retain  the  eggs  until  they  break  off 
from  the  chain,  but  void  them,  as  do  flukes. 

Fig.  93.   An  egg  of  fish  through  the  genital  pore.     The  empty  pro- 
tapeworm,  Z). /a^ws, —  note      lii-j        1         1  jj.-i.j  ui 
segmented  condition  and  glottids,  shrunken  and  twisted,  are  broken 

operculum;  5,  ciliated  em-  off  in  short  chains  from  time  to  time. 
300?  UfTe^Looss.)^  ''''*  The  eggs  (Fig.  93 A),  which  are  large  and 
brown  with  a  lid  at  one  end  as  in  fluke 
eggs,  contain  six-hooked  embryos  which  are  furnished  with  a 
covering  of  cilia  (Fig.  93B).  The  eggs  hatch  in  water  in  from  eight 
to  fifteen  days,  and  the  embryos  swim  about  by  means  of  their 
cilia,  though  they  often  slip  out  of  their  ciliated  envelope  and 
creep  on  the  bottom.  The  embryos  have  recently  been  shown 
by  Rosen  and  by  Janicki  to  develop  in  certain  species  of  Cyclops 
and  Diaptomus,  copepod  crustaceans,  into  larvsG  which  are 
called  procercoids.  In  12  to  15  days  these  larvae  are  about  0.4 
mm.  (eo  of  an  inch)  in  length,  sausage  shaped,  with  a  spherical 
caudal  appendage  carrying  the  embryonic  hooks.     This  append- 


LARVAL  TAPEWORMS  IN   MAN  247 

age  shrinks  and  a  depression  appears  at  the  opposite  end;  a 
large  portion  of  the  body  is  occupied  by  a  pyriform  central  mass. 
The  full  development  is  reached  in  two  or  three  weeks,  the  larvae 
being  then  about  0.5  mm.  long.  Small  trout  fed  on  the  infected 
cope  pods  were  successfully  infected.  The  passage  through  the 
intestine  and  body  cavity  of  the  fish  is  slow;  it  requires  about  six 
days  for  the  larvae  to  reach  the  liver  in  young  fish,  and  in  older 
fish  it  may  take  from  two  to  four  weeks.  In  the  fish  the  worms 
develop  into  plerocercoid  larvae  in  the  muscles.  Pike,  perch  and 
other  carnivorous  fish  are  most  frequently  infected. 

When  eaten  by  a  susceptible  host  in  raw  or  imperfectly  cooked 
fish,  the  larva,  except  the  head,  is  digested,  and  the  head,  at- 
taching itself  to  the  wall  of  the  small  intestine,  begins  to  grow 
into  an  adult  worm  at  the  rate  of  about  31  to  32  proglottids  a 
day.  The  mature  eggs  begin  to  appear  in  the  faeces  within  a 
month. 

The  fish  tapeworm  is  especially  active  in  the  production  of 
toxins  which  cause  intense  anemia.  Its  head  has  been  found 
to  produce  oleic  acid,  a  substance  which  has  blood-destroying 
properties.  Often  the  nervous  symptoms  produced  by  this 
species  are  also  very  marked. 

Two  other  species  of  Dibothriocephalidae  have  been  found  in 
man.  One  of  these,  Diphyllobothrium  cordatus  (Figs.  84G  and 
87D),  occurs  in  dogs,  seals  and  other  fish-eating  animals  in  Green- 
land. It  only  accidentally  establishes  itself  in  man.  Diplo- 
gonoporus  grandis  is  a  very  large  species,  found  in  Japan,  in 
which  there  is  a  double  set  of  reproductive  organs.  The  genital 
openings  are  arranged  in  two  longitudinal  grooves  on  the  ventral 
side  of  the  worm  (Fig.  84F).     This  species  is  rare  in  man. 


Larval  Tapeworms  in  Man 

There  are  several  species  of  tapeworms  which  inhabit  the  human 
body  in  the  larval  or  bladderworm  stage.  Three  types  are  found 
in  man.  Most  important  are  the  huge  multiple  cysts  or  "  hyda- 
tids "  of  Echinococcus  granulosus ^  a  small  tapeworm  of  dogs. 
Second,  there  are  the  bladderworms  of  the  common  pork  tape- 
worm, Tcenia  solium,  which  often  occur  in  large  numbers,  and 
may  be  of  very  serious  nature  if  located  in  important  organs. 
And,  finally,  there  are  two  species  of  Sparganum.     This  is  not 


248  THE  TAPEWORMS 

a  true  genus  but  is  a  collective  group  of  larval  tapeworms  of  the 
plerocercoid  type  which  cannot  be  definitely  classified  because 
the  adult  is  unknown. 

Echinococcus  hydatids.  —  In  some  parts  of  the  world  infection 
with  the    hydatids  or    larvae  of  Echinococcus  is  very  common, 
especially  in  children.     In  Iceland,  where  there  is  very  close  asso- 
ciation between  the  human  and  the  canine  population,  two  or 
three  per  cent  of  the  inhabitants  are  afflicted,  and  in  certain  dis- 
tricts as  high  as  ten  per  cent.     In  Australia,  also,  this  tapeworm 
is  common  in  dogs  and  its  larvae  occur  in  a  considerable  pro- 
portion of  human  beings  as  well  as  in  stock.     In  the  United 
States,  especially  in  the  southeastern  states,  it  is  fairly  common. 
The  adult  of  Echinococcus  (Fig.   94)   is  a  minute  tapeworm 
found  in  dogs  and  sometimes  in  other  carnivorous  animals.     It 
measures  only  from  one-tenth  to  one-fifth  of  an  inch  in  length. 
The  mature  worm  consists  of  a  tiny  scolex  with  four  suckers  and 
a  double  crown  of  hooks,  followed  by  an  unsegmented  neck  and 
three  gradually  larger  proglottids,  the  ultimate 
one  of  which  is  larger  than  all  the  rest  of  the 
worm  and  contains  about  500  eggs  in  the  uterus. 
Echinococcus  may  occur  in  hundreds  or  even 
thousands  in  the  intestine  of  dogs,   though  it 
often  escapes  notice  on  account  of  its  small  size. 
The  eggs  of  the  worm,  dropped  in  pastures 
with  the  faeces  of  infected  dogs,  ordinarily  de- 
velop   in    sheep,    cattle    or    other    herbivorous 
animals.     Human  infection  usually  results  from 
too  intimate  association  with  dogs,  and  children 
especially  are  liable  to  infection  by  allowing  dogs 
Fig  94    Ech'    _  ^^  "  ^^^^  "  them  or  Hck  their  faces  with  a  tongue 
coccus    granulosus  which,  in  view  of  the  unclean  habits  of  dogs, 
(After^Leuck^t^)^   ^^^  ^®  ^^  efficient  means  of  transmission  for 
the  tapeworm  eggs. 
The  hydatids  develop  in  many  different  organs  of  the  body. 
The  liver  is  the  favorite  site,  after  which,  in  order  of  frequency, 
come   the  lungs,   kidneys,   spleen,   intestinal   walls,   membranes 
lining  the  body  cavity,  heart,  brain  and  various  muscles.     Some- 
times a  single  host  is  invaded  by  the  hydatids  in  several  different 
organs. 
The  development  of  the  embryos  is  very  slow  indeed.     In  a 


ECHINOCOCCUS  HYDATIDS  249 

month  after  reaching  their  destination  in  the  hver  or  other  organs 
they  are  in  the  form  of  Httle  globular  bodies,  enclosed  by  a  cap- 
sule produced  at  the  expense  of  the  host.  A  cyst  measures  about 
one  mm.  (2^5  of  an  inch)  in  diameter.     By  the  end  of  the  fifth 


Fig.  95.     Diagram  of  portion  of  small  Echinococcus  cyst  showing  daughter  cyst 
(d.c),  brood  capsules  (br.  cap.)  and  invaginated  heads  (h.).    X  about  5. 

month  it  has  grown  to  the  size  of  a  walnut.  The  membrane  of 
the  bladderworm  itself  is  very  delicate,  but  the  capsule  formed 
by  the  host  is  thick  and  tough.  The  enclosed  fluid  is  transparent 
and  nearly  colorless,  and  is  composed  of  various  materials  which 
have  permeated  in  from  the  blood  and  tis- 
sues of  the  host,  and  of  the  waste  products 
produced  by  the  growth  of  the  parasite. 

When  the  hydatid  has  reached  this  stage 
in  its  development  (Fig.  95)  there  grow 
into  its  cavity  from  the  inner  surface  little 
vesicles  or  brood  capsules,  on  the  inner  sur- 
face of  which  in  turn  there  grow  a  number  of 
little  heads  or  scoleces.  Each  of  the  heads 
has  the  power  ultimately  to  grow  into  an 
adult  worm.  As  there  may  be  a  dozen  or 
more  of  the  scol ex-bearing  brood  capsules  in  cyst  from  liver  of  steTr.^f 
a  single  hydatid,  and  from  six  to  30  heads  nat.size.  (After  Ostertag 
in  a  single  vesicle,  the  number  of  heads  of  ^°™ 
scoleces  produces  may  be  enormous.  Sometimes  there  may  be 
still  further  multiplication  by  the  development  of  secondary  cysts 
either  inside  or  outside  of  the  original  hydatid  which  may  develop 
a  whole  series  of  scolex-bearing  vesicles  of  their  own. 

Sometimes  instead  of  forming  the  usual  large  vesicles  and 
secondary  vesicles,  the  growth  results  in  the  formation  of  a  great 
mass  of  small  separate  vesicles  (Fig.  96),  varying  in  size  from  a 


250 


THE  TAPEWORMS 


pinhead  to  a  pea,  with  few  and  scattered  heads.  These  masses 
of  vesicles,  known  as  ''  multilocular  "  cysts,  may  be  six  inches 
or  more  in  diameter;  they  are  most  frequently  found  in  the  liver. 
Unless  surgically  removed  they  usually  prove  fatal  sooner  or  later. 
The  fact  that  the  "  multilocular  "  cysts  are  not  found  in  Ice- 
land or  Australia  where  the  ordinary  cysts  are  so  common,  and 
that  they  occur  to  the  almost  total  exclusion  of  the  ordinary 
kinds  in  some  countries,  especially  in  parts  of  Germany,  suggests 
that  they  may  belong  to  a  different  species  indistinguishable 
from  E.  granulosus  in  the  adult  state. 

The  great  size  to  which  hydatids  may  grow  makes  them  danger- 
ous on  account  of  the  mere  mechanical  damage  they  may  do, 
especially  if  they  occur  in  such  organs  as  the  heart,  brain,  kid- 
neys or  liver.     The  liver  of  an  ox  containing  hydatids  has  been 

known  to  reach  ten  times  its  normal 
weight,  and  to  be  of  such  large  size 
as  to  cause  much  mechanical  injury 
to  neighboring  organs.  But  more 
dangerous  than  the  mechanical  injury 
is  the  possibility  that  the  vesicles, 
hemmed  in  by  restraining  tissues,  may 
burst  and  liberate  into  the  tissues  the 
poison-bearing  liquid  which  fills  them. 
Hydatids  may  grow  persistently  for 
many  years.  There  is  one  case  on 
record  where  a  swelling  had  gradually 
developed  during  43  years  over  a  large 
Fig.  97.  Echinococcus  cyst  portion  of  the  face  of  a  woman,  and 
in  liver  of  man.    (After  Huber  ^^s  as  large  as  a  child's  head.     When 

from  Stiles.)  ,    ,  , .  , ,  . 

removed  by  an  operation,  this  was 
found  to  be  a  hydatid.  Ordinarily  growth  does  not  increase 
beyond  the  size  of  a  baseball.  The  only  treatment  is  a  surgical 
operation. 

The  conditions  which  exist  in  places  where  hydatid  disease  in 
man  is  common  gives  us  an  idea  of  what  to  avoid  in  order  to  pre- 
vent infection.  In  Iceland  from  30  to  100  per  cent  of  the  dogs  in 
different  regions  are  said  to  be  parasitized  by  Echinococcus.  A 
large  proportion  of  the  sheep  and  many  cattle  are  infested  with 
the  hydatids.  The  dogs  are  fed  on  the  uncooked  entrails  and 
waste  meat  of  slaughtered  animals,  and  the  dogs  in  turn  are 


CYSTICERCUS  CELLULOSE  251 

allowed  to  run  at  will  over  the  pastures,  dropping  the  egg-laden 
proglottids  with  the  faeces  in  places  where  the  water  or  food  of 
the  stock  may  be  infected.  Dogs  are  allowed  the  free  run  of 
the  houses,  are  given  unbounded  liberty  in  playing  with  children, 
and  not  infrequently  eat  from  the  same  dish  as  their  human 
companions.  The  resulting  prevalence  of  Echinococcus  in  both 
dogs,  stock  and  man  is  hardly  to  be  wondered  at. 

The  precautions  which  should  be  taken  to  prevent  the  spread 
and  to  bring  about  the  control  of  this  disease  may  be  summar- 
ized as  follows:  (1)  avoidance  of  too  great  familiarity  with 
dogs,  (2)  exclusion  of  dogs  from  shores  of  lakes  or  reservoirs  from 
which  drinking  water  is  taken,  (3)  extreme  cleanliness  in  handling 
of  food,  (4)  prevention  of  dogs  from  eating  the  entrails  or  meat 
scraps  of  animals  which  may  be  infected  with  hydatids. 

Cysticercus  of  Taenia  solium,  —  The  fact  that  the  bladder- 
worms  of  the  pork  tapeworm,  Tcenia  solium,  sometimes  occur  in 
man  has  already  been  mentioned.  Since  self-infection  with  the 
eggs  of  the  worm  is  a  dangerous  possibility,  the  presence  of  a 
pork  tapeworm  in  the  intestine  is  to  be  looked  upon  much  more 
seriously  than  infection  with  other  tapeworms. 

The  bladderworms,  technically  named  Cysticercus  celluloses 
(Fig.  86 A),  develop  from  the  six-hooked  embryos  which  are 
freed  from  t»he  enclosing  egg-shell  by  the  gastric  juices.  The 
embryos  bore  through  the  intestinal  wall  and  migrate  to  various 
organs  and  tissues  to  develop. 

The  effect  of  Cysticercus  infection  depends  entirely  upon  the 
number  present  and  upon  their  location  in  the  body.  A  few  of 
them  in  the  muscles  or  in  the  connective  tissue  under  the  skin  are 
quite  harmless.  In  the  eye,  heart,  spinal  cord,  brain  or  other 
delicate  organs  their  presence  may  be  very  serious,  the  symptoms 
being  due  chiefly  to  mechanical  injury.  Infection  of  the  brain 
is  usually  accompanied  by  epileptic  fits,  convulsions  and  other 
nervous  disorders.  There  is  no  treatment  except  a  surgical 
operation,  and  this  is  often  obviously  impossible,  both  on  account 
of  the  number  and  position  of  the  parasites.  Moreover,  in  a 
great  many  cases  a  correct  diagnosis  of  this  infection  is  made  only 
in  a  post-mortem  examination. 

Sparganum.  —  The  group  name  Sparganum  has  been  given  to 
plerocercoid  larvae  of  tapeworms  of  the  family  Dibothriocepha- 
lidae,  of  which  the  adult  form  is  unknown  and  the  true  genus  there- 
fore indeterminable. 


252 


THE  TAPEWORMS 


The  most  common  type  of  such  tapeworm  larvae  is  Sparganum 
mansoni  (Fig.  98),  an  elastic  worm  three  to  14  inches  in  length. 
It  is  not  segmented,  but  appears  so  since  it  is 
transversely  wrinkled;  there  is  an  invaginated 
scolex  at  the  broader  end.  These  parasites  are 
found  coiled  in  the  connective  tissue  of  man 
and  other  animals,  often  causing  tumors.  The 
majority  of  human  cases  have  occurred  in  Japan, 
but  cases  are  recorded  from  many  other  parts 
of  the  world  also,  including  Texas. 

Recently  it  has  been  shown  that  this  worm 
is  the  larva  of  Diphyllobothrium  mansoni  of  dogs 
and  cats,  which  has  a  life  history  similar  to  that 
of  D.  latus.  The  first  larva,  or  procercoid, 
develops  in  Cyclops  leuckarti,  but  not  in  related 
copepods.  The  plerocercoid  or  sparganum  stage 
develops  in  a  large  number  of  different  animals, 
including  man,  but  probably  the  normal  second 
intermediate  hosts  are  cold-blooded  vertebrates, 
especially  frogs  and  snakes,  in  which  they  are 
very  common.  When  these  animals  are  eaten 
by  dogs  or  cats  the  parasite  completes  its  de- 
velopment to  the  adult  form. 

Another  type  of  Sparganum,  which  has  been 
termed  S.  proUferum,  was  discovered  by  a 
Japanese  investigator,  Ijima,  in  a  Japanese 
woman  in  1904.  The  skin  on  a  large  part  of 
her  body  was  much  swollen  and  presented 
numerous  hard  pimples.  Examination  showed 
thousands  of  worms  which  were  identified  as 
larval  tapeworms  of  the  Sparganum  type, 
imbedded  in  little  oval  capsules  varying  in  size  from  less 
than  one  mm.  (-^^  of  an  inch)  in  length  to  six  or  eight 
mm.  (i  of  an  inch).  Young  slender  worms  not  yet  encysted  were 
also  found.  In  1907  a  similar  case  occurred  in  a  fisherman  in 
Florida,  and  the  parasites  were  believed  by  Dr.  Stiles  to  be  either 
identical  with  or  closely  related  to  the  Japanese  worm.     Two 


Fig.  98.  Spar- 
ganum mansoni; 
nat.  size.  (After 
Ijima  and  Mur- 
ata.) 


SPARGANUM  PROLIFERUM 


253 


other  Japanese  cases,  discovered  in  1907  and  1911  respectively, 
have  also  been  reported.  In  one  of  these  the  worms,  most  but 
not  all  of  them  in  capsules,  were  found  in  countless  numbers  not 
only  in  the  subcutaneous  tissue  but  also  in  the  muscles  and  through- 
out most  of  the  internal  organs,  including  even  the  brain. 

The  worms  of  this  species  (Fig.  99)  are  in  all  cases  white,  flat- 
tened organisms  of  very  variable  shape  and  size.  They  usually 
vary  from  three  mm.  to  12  mm.  (|  to  ^  an  inch)  in  length,  and 
from  0.3  mm.  to  2.5  mm.  (go  to  lo  of  an  inch)  in  width,  but  in 
one  Japanese  case  they  were  uniformly  larger,  reaching  a  length 
of  three  inches.  Their  peculiarly  irregular  shape  is  due  to  the 
unique  method  of  proliferation  by  the  growth  of  buds  or  super- 
numerary heads.  These  apparently 
become  detached,  leave  the  cyst,  and 
become  encapsuled  themselves  after 
migrating  in  the  subcutaneous  tissue. 
This  explains  the  increasing  num- 
bers of  acne-like  spots  or  nodules 
containing  worms,  which  were  re- 
ported by  the  patients. 

Attempts  made  by  Ijima  to  pro- 
duce adult  worms  by  feeding  the 
larvae  to  various  domestic  animals 
failed,  and  nothing  is  known  of  the 
life  history  or  mode  of  infection  be- 
yond a  suspicion  that  the  eating  of 
raw  fish  is  responsible  for  it.     Dr. 

^  ,  ,.  1    J.1        T-n      "J  Fig.  99.     Sparganum  proliferum, 

Gates,   who   discovered  the  l^lorida  from  man  in  Florida.    Much  en- 
case, reported  that  there  was  probably  larged.    (After  stiles.) 
a  similar  case  in  Florida  a  few  years 

before,  the  patient  having  moved  to  California  where  he  died 
*' eaten  up  with  worms." 

The  rare  occurrence  of  this  peculiar  and  serious  parasitic  disease 
is  evidence  that  the  mode  of  infection  is  unusual.  The  suspicion 
that  it  results  from  eating  raw  fish  is  sufficient  reason  for  discrim- 
ination against  c^his  kind  of  food  even  in  places  where  this  or  other 
human  para  sites  which  come  from  raw  fish  are  not  positively 
known  to  occur. 


CHAPTER  XIV 
HOOKWORMS 

History.  —  For  many  years  it  was  customary  in  the  United 
States  to  look  upon  the  shiftless  people  to  be  found  in  our  South 
as  the  product  of  wanton  laziness  and  an  inborn  lack  of  ambition. 
For  decades  the  more  fortunate  Northerners  considered  the 
"  poor  whites  "  of  the  South  a  good-for-nothing,  irresponsible 
people,  worthy  only  of  scorn  and  of  the  sordid  poverty  and  ig- 
norance which  they  brought  upon  themselves  as  the  fruits  of 
their  own  shiftlessness.  When  it  became  known,  largely  as  the 
result  of  investigations  by  Dr.  C.  W.  Stiles,  of  the  U.  S.  Public 
Health  Service,  that  these  hopelessly  incapable  and  pitifully 
emaciated  and  stunted  people  were  the  victims,  not  of  their  own 
unwillingness  to  work  or  learn,  but  of  the  attacks  of  intestinal 
worms  which  sapped  their  vitality,  poisoned  their  systems,  and 
stunted  both  their  mental  and  physical  growth,  and  that  over 
two  million  people  in  our  own  southern  states  were  the  victims  of 
these  parasites,  the  "  poor  whites  "  and  "  lazy  niggers  "  of  the 
South  became  objects  of  pity  and  help  rather  than  of  scorn. 

The  hookworm,  which  is  the  cause  of  this  deplorable  condition, 
is  by  no  means  a  newly  discovered  parasite.  A  close  cousin  of 
the  American  hookworm  was  discovered  in  Italy  over  75  years 
ago,  and  has  subsequently  been  found  to  be  prevalent  in  parts  of 
every  warm  country  in  the  world,  in  some  places  infesting  nearly 
or  quite  100  per  cent  of  the  inhabitants.  It  would  probably  be 
well  within  the  truth  to  say  that  over  half  a  billion  people  in  the 
world  are  infected  with  hookworms.  The  disease  caused  by 
hookworm,  which  has  recently  come  to  be  used  as  a  symbolism 
for  laziness,  was  known  for  ages  before  the  cause  of  it  was  dis- 
covered, in  fact  it  was  probably  one  of  the  ailments  most  familiar 
to  the  ancient  Egyptians,  and  descriptions  of  symptoms  probably 
representing  hookworm  disease  appear  in  the  medical  papyrus 
of  3500  years  ago.  The  disease  has  gone  by  many  names: 
malcoeur  or  mal  d'estomac  in  the  West  Indies,  tuntun  in  Colombia, 

254 


DESCRIPTION  OF  SPECIES  255 

opilag9o  in  Brazil,  tunnel  disease  and  miner's  itch  in  Europe, 
and  chlorosis  in  Egypt. 

The  American  hookworm,  Necator  americanus,  was  probably 
introduced  into  America  from  Africa  by  slaves.  In  many  parts 
of  the  latter  continent  as  well  as  in  parts  of  Asia,  especially 
Ceylon,  this  hookworm  is  very  common.  It  occurs  in  the 
gorilla  as  well  as  in  man.  In  the  United  States  it  is  occasionally 
found  in  all  but  the  most  northern  states,  but  is  a  great  menace 
only  in  the  southern  ones  —  North  and  South  Carolina,  Georgia, 
Florida,  Alabama,  Mississippi,  Louisiana  and  Texas.  It  also 
presents  a  serious  problem  in  Cuba,  Porto  Rico  and  Brazil.  In 
most  other  warm  parts  of  the  world  a  closely  allied  species,  the 
Old  World  hookworm,  Ancylostoma  duodenale,  is  more  prev- 
alent. It  is  impossible  now  to  know  what  was  the  origin  or 
natural  distribution  of  either  species,  since  both  worms  have 
been  introduced  by  infected  travelers  into  every  quarter  of  the 
globe.  In  Europe  Ancylostoma  duodenale  is  far  the  more  com- 
mon. It  first  attracted  attention  there  as  the  cause  of  "  tunnel 
disease  "  at  the  time  of  the  building  of  the  St.  Gothard  tunnel. 
The  infected  laborers,  dispersing  after  the  completion  of  the 
tunnel,  spread  the  infection  to  all  parts  of  Europe,  and  serious 
epidemics  broke  out  in  the  coal-mining  districts  of  Hungary, 
Germany  and  Belgium. 

The  Parasites.  —  The  two  species  of  human  hookworms  are 
similar  in  structure;  they  agree  in  all  important  details  of  life 
history;  and  both  produce  the  same  symptoms,  require  the 
same  treatment,  and  can  be  prevented  in  the  same  ways.  They 
are  round  worms,  belonging  to  the  great  group  of  nematodes, 
which  as  adults  live  in  the  small  intestine  of  their  hosts  and  suck 
blood.  An  allied  species,  A.  ceylanicum,  found  in  civet  cats  and 
dogs  in  southern  Asia  occasionally  occurs  in  man.  The  American 
hookworm,  Necator  americanus  (Fig.  100),  is  smaller  than  the 
Old  World  species,  Ancylostoma  duodenale,  the  measurements 
being  about  eight  mm.  (one-third  of  an  inch)  and  ten  mm.  (two- 
fifths  of  an  inch)  respectively  in  the  males,  and  ten  mm.  and  15 
mm.  (three-fifths  of  an  inch)  respectively  in  the  females.  They 
are  normally  whitish  in  color  but  when  gorged  with  blood  they 
are  reddish  brown.  The  females,  which  are  much  more  numerous 
than  the  males,  have  simple  cylindrical  bodies,  largely  occupied 
by  the  threadlike  ovaries  and  egg-filled  oviducts.     In  the  Old 


256 


HOOKWORMS 


World  species  the  mouth  (Fig.  101  A)  is  armed  with  a  number  of 
chitinous  hooklike  teeth,  which  in  the  American  species  are 
replaced  by  hard  ridges  or  lips  (Fig.  lOlB).     The  male  worms  are 


U 


Am.  Hookworm 
not,  size 


Qld  World  ttookwor/i* 
ntft.S'ue 

Fig.  100.  American  hookworm,  Necator  americanus,  male  {$)  and  female  ( 9) ; 
b.c,  buccal  cavity;  ph.,  pharynx;  int.,  intestine;  cerv.  gl.,  cervical  gland;  t., 
testis;  sp.  d.,  sperm  duct;  b.,  bursa;  ov.,  ovaries  and  oviducts;  v.,  vulva  or 
genital  opening;   a,  anus.      X  8.     (Partly  after  Manson.) 

also  cylindrical  but  instead  of  tapering  at  the  tail  end  they  possess 
an  umbrella-like  expansion  known   as  a  bursa,   which  is  sup- 


FiG.  101.  Buccal  cavity  and  mouth  of  Old  World  hookworm  (A),  and  American 
hookworm  (J5),  showing  teeth  in  former  and  cutting  ridges  in  latter.  A,  X  100; 
B,   X  230.     (After  Looss.) 

ported  by  clawlike  rays  somewhat  suggestive  of  the  ribs  of  an 
umbrella  (Fig.  102).  The  bursa  is  used  for  holding  the  female 
during  copulation.     It  was  the  clawlike  ribs  of  this  '*  umbrella '' 


LIFE  HISTORY 


257 


which  first  suggested  the  name  "  hookworm  "  for  the  parasites, 
though  the  hookhke  teeth  in  the  mouth  of  the  Old  World  species 
might  just  as  readily  have  suggested  the  name. 


Fig.  102.     Bursa  of  American  hookworm.     (After  Stiles.) 


B(XI50) 


Fig.  103.  Life  history  of  hookworm;  A,  adults,  female  and  male,  in  intestine; 
B,  egg  as  passed  in  faeces;  C,  embryo  hatching  in  ground,  24-48  hours  later;  D, 
fully  developed  larva,  enclosed  in  sheath,  ready  to  infect  human  being;  E,  larvae 
released  from  sheath,  migrating  in  body  of  new  host. 

Life  History.  —  (Fig.  103.)  The  female  worms  produce  an 
enormous  number  of  eggs  which  are  poured  into  the  intestine  of 


258  HOOKWORMS 

the  host,  usually  in  a  continuous  stream,  but  occasionally  with 
intermissions,  to  be  passed  with  the  faeces.  The  thin-shelled 
eggs,  which  are  about  60  /x  by  35  ^  (4^ ^  by  ^^^  of  an  inch)  in  size, 
and  sHghtly  larger  in  the  American  species,  undergo  the  first 
stages  of  development  while  still  in  the  intestinal  canal,  and  by 
the  time  they  are  voided  with  the  faeces  they  are  segmented  into 

from   two   to    eight    cells 

C£^)  (Fig.  104).  The  segmented 

condition,  together  with 
the  fact  that  they  are  clear 
and  not  yellow  or  brown 
from  bile  stain,  distin- 
guishes the  eggs  from  those 
of  many  other  worms 
T,     ,^,     ^        ,,     ,  .        ,  found    in    the    intestine. 

J^iG.  104.     liiggs  of  hookworms  in  early  stages  -^,111 

of    segmentation,— four-segmented   type   most  Further  development  doeS 

common  in  faeces;    A,  Necator  americanus;    B,  ^^^    ^^]^q    ^I^^q    ^^^^l    ^^^ 

Ancylostoma  duodenale.  ^ 

faeces  are  exposed  to  air, 
when,  if  moisture  is  present  and  the  temperature  is  moderately  high 
(65°  to  85°  F.),  the  development  continues  and  the  embryo  hatches 
in  from  24  to  48  hours  (Fig.  103C).  Below  65°  F.  development  is 
very  slow,  and  above  85°  F.,  although  development  is  very  rapid, 
the  eggs  and  larvae  are  likely  to  die.  The  newly  hatched  worm  is 
about  0.2  mm.  (less  than  a  hundredth  of  an  inch)  in  length  with  a 
bottle-shaped  oesophagus,  a  simple  intestine,  and  practically  no  re- 
productive organs.  The  most  favorable  conditions  for  the  devel- 
opment of  the  larvae,  in  addition  to  the  temperatures  mentioned, 
are  a  moderate  degree  of  moisture,  presence  of  air,  plenty  of  food 
in  the  form  of  decomposing  organic  matter,  and  not  too  rapid 
putrefaction.  According  to  Looss,  the  larvae  will  not  develop 
well  in  faeces  derived  from  a  purely  vegetable  diet,  a  small  propor- 
tion of  animal  matter  being  essential  for  food.  Enough  animal 
food  for  some  development  would  always  be  provided  by  blood 
from  intestinal  hemorrhages.  On  the  other  hand  a  purely  meat 
diet  is  unfavorable  on  account  of  the  rapid  putrefaction.  If 
suitable  conditions  are  present,  the  larva  grows  rapidly  for  four 
or  j&ve  days,  shedding  its  skin  at  the  end  of  the  second  day.  In 
about  five  days,  under  ideal  conditions,  the  skin  begins  to  be- 
come detached  again  but  is  not  shed.  It  is  retained  as  a  flexible 
protecting  sheath  for  the  larva,  but  does  not  hinder  free  motion 


MODE  OF  INFECTION  259 

(Fig.  103D).  The  larva  has  by  this  time  grown  to  several  times 
its  original  size,  being  over  5  mm.  (sV  of  an  inch)  in  length,  and  is 
now  in  the  infective  stage  and  ready  to  begin  its  parasitic  life. 
No  further  food  is  taken  but  the  parasite  begins  an  active  migra- 
tion in  the  neighboring  soil  or  water.  If  even  a  trace  of  moisture 
is  present  in  the  soil  the  larvse  are  capable  of  traversing  consider- 
able distances  and  may  thus  give  rise  to  infection  far  from  the 
place  where  the  faeces  were  originally  deposited.  They  are  said 
to  be  able  to  travel  through  moist  soil  at  a  rate  of  probably  not 
less  than  five  feet  per  hour,  which,  if  kept  up  constantly  in  a 
straight  hne  would  mean  a  wandering  of  forty  yards  in  twenty- 
four  hours.  While  such  continued  travel  in  a  straight  line  prob- 
ably would  never  occur,  it  is  evident  that  a  single  infective  stool 
would  easily  be  able  to  infect  the  ground  for  several  square  yards. 
Complete  drying  up  is  fatal  to  both  eggs  and  larvse  in  all  stages. 

The  larvae  may  remain  just  under  the  surface  of  moist  soil  or 
mud  or  in  water  for  a  long  time,  awaiting  an  opportunity  to  enter 
a  human  host.  They  have  been  kept  alive  in  the  laboratory 
in  plain  water  at  a  temperature  of  about  60°  F.  for  18  months 
and  unless  attacked  by  predaceous  insects  or  other  animals 
would  undoubtedly  live  fully  as  long  under  outdoor  conditions. 
They  are  much  more  resistant  to  unfavorable  conditions  than 
are  the  eggs  or  newly  hatched  larvae.  They  can  exist  under  de- 
privation of  air  for  a  long  time  and  may  survive  burial  in  snow 
for  at  least  six  days. 

It  was  formerly  thought  that  infection  occurred  by  way  of  the 
mouth  only,  the  larvae  entering  with  impure  food  or  water.  It 
is  now  believed,  however,  that  this  means  is  not  only  not  the 
usual  one,  but  that  direct  infection  by  swallowing  may  never 
occur,  since  there  is  evidence  to  show  that  the  parasites  are  un- 
able to  resist  the  acid  juices  of  the  stomach  before  they  have 
first  passed  through  the  blood  and  tissues  of  tKe  body.  It  was 
discovered  purely  by  accident  that  the  hookworm  larvae  can 
readily  penetrate  the  skin  and  bore  through  the  tissues  until 
they  reach  a  vein.  The  feet  of  plantation  laborers  are  often  in 
a  bad  state  of  soreness  and  ulceration  due  to  the  boring  of  the 
larvae  and  to  subsequent  infection  by  bacteria.  Walking  on  in- 
fected ground  with  bare  feet  is  undoubtedly  the  mode  of  infection 
in  the  majority  of  cases.  By  the  blood  or  lymph  vessels  the 
worms  are  carried  eventually  to  the  heart  and  thence  to  the  lungs; 


260  HOOKWORMS 

from  the  lungs  they  pass  by  way  of  the  trachea  to  the  oesophagus, 
and  thence  to  the  stomach  and  intestine.  Experiments  show, 
however,  that  the  larvae  may  reach  the  intestine  by  other  routes, 
leaving  the  trachea  and  oesophagus  out  of  the  circle  of  migration, 
but  in  any  case  they  follow  a  rather  roundabout  path  in  the 
bloodvessels.  Probably  in  cases  of  infection  by  food  or  drink 
the  worms  bore  through  the  mucous  membranes  of  the  mouth  or 
oesophagus  during  the  swallowing  of  the  food  and  thus,  even 
when  eaten,  reach  their  ultimate  destination  by  an  indirect  route. 
The  larvae  shed  their  skins  twice  more  after  entering  the  human 
body,  each  time  attaining  more  and  more  of  the  adult  character- 
istics and  growing  in  size  at  the  expense  of  the  blood  and  mucous 
membranes  on  which  they  feed.  After  the  last  moult  the  sexes 
are  differentiated  but  the  larvae  are  still  less  than  a  fourth  their 
full  size  and  require  five  or  six  weeks  from  the  time  of  infection 
to  become  fully  mature.  The  length  of  life  of  individual  hook- 
worms in  the  intestine  is  variously  estimated  in  months  or  years. 
The  readiness  with  which  reinfection  usually  occurs  makes  this  a 
difficult  point  to  determine. 

The  Disease.  —  The  disease  to  which  hookworms  give  rise 
varies  to  a  very  great  extent  in  different  individuals,  and  is  not 
always  dependent  upon  the  number  of  worms  present.  It  was 
formerly  supposed  that  the  anemia  and  loss  of  vitality  produced 
by  hookworms  was  due  solely  to  the  loss  of  blood  devoured  by 
the  parasites.  In  cases  of  severe  infection,  where  perhaps  several 
thousands  of  worms  may  be  harbored  by  a  single  patient,  the 
amount  of  blood  devoured  must  be  sufficient  to  account  for  a 
considerable  degree  of  anemia.  However,  in  cases  of  infection 
with  relatively  few  worms  the  symptoms  are  sometimes  fully  as 
marked  and  cannot  be  explained  on  this  basis.  The  injuries 
from  hookworm  infection  result  apparently  from  a  number  of 
causes  which  may  be  summed  up  as  follows:  (1)  ulceration  or 
infection  of  the  skin  from  wounds  made  by  the  boring  of  the 
parasites,  often  giving  rise  to  an  extensive  affection  of  the  feet 
in  the  form  of  pimples  or  sores  called  *'  ground  itch,''  "  water 
sores,"  etc.,  caused  partly  by  entrance  of  bacteria  into  the  wounds, 
and  partly  by  the  irritation  produced  by  the  boring  of  the  worms; 
(2)  loss  of  blood  devoured  by  the  parasites;  (3)  loss  of  blood  from 
the  bleeding  of  wounds  into  the  intestines,  sometimes  very  con- 
siderable, due  to  a  secretion  from  the  mouth  of  the  worm  which 


PATHOGENIC  EFFECTS  261 

prevents  the  coagulation  of  blood;  (4)  the  entrance  of  harmful 
bacteria  and  other  microscopic  organisms  into  the  wounds  made 
by  the  worms,  resulting  in  the  absorption  of  bacterial  toxins  and 
in  the  formation  of  dangerous  lesions;  (5)  a  thickening  and  de- 
generation of  the  mucous  walls  of 
the  intestine;  and  (6)  the  secretion 
of  poisonous  substances  or  toxins 
from  glands  in  the  heads  of  the 
worms.  These  poisonous  secre- 
tions, which  have  blood-destroying 
properties,  probably  account  for 
more  of  the  symptoms  of  hook- 
worm disease  than  does  anything 
else,  though  apparently  they  have 
widely  different  effects  on  different 
individuals.     Sometimes  the  pres-      Fig.  io5.    American  hookworm; 

.        ,       «  •     J 1  1       section  showing  manner  of  attach- 

ence  of  eggs  m  the  tseceS  is  the  only    ^ent    to    intestinal    wall.       (After 

indication  of  infection.    Negroes  as  Ashford  and  igaravidez,  from  photo 

1  u  f        1  4.-U-T4.       ^y  ^^-  W-  ^-  Gray.) 

a  class  show  tar  less  susceptibility 

to  the  poisons  produced  by  hookworms  than  do  the  whites;  this 
is  especially  well  demonstrated  in  our  southern  states.  The 
symptoms  are  more  severe  in  summer  than  in  winter,  very 
probably  due  to  the  greater  abundance  of  worms  in  the  summer. 

Hookworm  disease  is  almost  always  preceded  by  a  case  of 
ground  itch,  due,  as  remarked  above,  to  irritation  from  the  boring 
of  the  worms  and  to  secondary  infection  with  bacteria.  The 
commonest  symptom  of  the  disease  is  anemia,  usually  accom- 
panied by  some  fever  or  dyspeptic  trouble,  though  often  in  mild, 
cases  there  is  no  evident  emaciation.  The  significant  name  "  el 
palido  "  (the  pale  one)  is  applied  to  the  hookworm  victim  on  the 
coffee  plantations  of  Porto  Rico.  In  severe  cases  of  long  stand- 
ing the  anemia  and  loss  of  vitality  become  extreme  and  so  weaken 
the  patient  that  he  succumbs  to  the  least  unfavorable  circum- 
stance; his  unhappy  career  is  usually  ended  by  some  slight  illness 
which  in  normal  health  he  could  easily  have  resisted.  In  Porto 
Rico  about  30  per  cent  of  all  deaths  are  attributed  to  hook- 
worm. 

Both  the  mental  and  physical  development  become  abnormal. 
A  child  of  12  or  14  years  may  have  the  degree  of  development 
which  should  belong  to  an  average  child  of  six  or  eight  and  a 


262  HOOKWORMS 

young  man  or  woman  of  20  may  present  the  general  development 
of  a  child  of  12  or  14,  though  the  face  may  appear  either  very 
childish  or  prematurely  old.  Girls  who  are  affected  from  child- 
hood lack  development  of  the  breasts,  but  in  general  there  is  no 
marked  loss  of  flesh.  The  face  has  a  stupid  bloated  appearance, 
and  the  eyes  have  a  hollow  stare  which  is  very  characteristic. 
The  bloating  carried  to  the  abdomen  results  in  "  pot-belly." 
The  appetite,  at  first  ravenous,  diminishes  with  the  progress  of 
the  disease,  and  frequently  becomes  perverted  so  that  patients 
become  dirt-eaters,  i.e.,  have  a  mania  for  swallowing  earth  or 
mud,  possibly  a  reaction  involuntarily  prompted  by  the  irritation 
of  the  intestinal  tract  by  the  parasites.  Over  25  per  cent  of  the 
hookworm  patients  of  one  physician  in  our  southern  states  con- 
fessed to  '*  dirt-eating."  The  diseased  appetite,  of  course,  only 
adds  to  the  infection.  The  nervous  symptoms,  which  are  rather 
late  in  appearance,  consist  of  dizziness,  headache  and  profound 
stupidity. 

The  loss  of  efficiency  from  hookworm  infection  is  startling,  and 
the  slow  development  of  many  countries  may  be  largely  attributed 
to  the  handicap  placed  upon  the  citizens  by  the  hookworm.  The 
effect  of  the  disease  can  be  appreciated  from  the  following  ex- 
amples: the  managers  of  large  coffee  "  haciendas  "  in  Porto 
Rico  state  that  hookworm  reduces  the  average  efficiency  of  the 
laborers  from  35  to  50  per  cent.  On  a  cocoa  plantation  in 
Ecuador  not  over  33  per  cent  of  the  work  which  should  have  been 
obtained  from  300  laborers  was  available,  due  to  anemias  of 
hookworm  and  chronic  malaria.  On  a  sugar  plantation  in 
British  Guiana,  after  the  laborers  had  been  treated  for  hookworm 
on  a  large  scale,  the  working  power  of  the  gangs  increased  100 
per  cent.  Dr.  McDonald  of  Queensland,  Austraha,  reports  that 
hookworm  "  is  sucking  the  hearts'  blood  of  the  whole  com- 
munity." The  loss  of  efficiency  of  the  miners  in  a  single  Cali- 
fornia mine,  due  to  hookworm,  has  been  estimated  at  20  per  cent. 
Estimating  only  50  per  cent  of  the  miners  to  be  infected,  the 
annual  economic  loss  in  this  one  mine  would  be  $20,000  per  year. 
The  economic  loss  due  to  the  infection  of  2,000,000  or  more  people 
in  the  southeastern  United  States  or  to  the  infection  of  from 
60  to  80  per  cent  of  the  300,000,000  people  of  India  must  be 
almost  incalculable. 

The  retarding  effect  of  the  disease  in  education  and  civiHzation 


TREATMENT  263 

is  not  less  terrible.  There  are  many  families  in  our  South  where 
for  at  least  four  generations  illiteracy  and  ignorance  have  re- 
sulted from  disablement  by  hookworm  disease.  In  many  com- 
munities large  proportions  of  the  children  are  kept  out  of  school 
on  account  of  physical  or  mental  disablement  from  this  cause. 
Unlike  many  diseases,  this  one  has  no  tendency  to  weed  out  the 
weak  and  unfit;  it  works  subtly,  progressively,  undermining 
the  physical  and  intellectual  life  of  the  community,  each  gener- 
ation handing  down  an  increased  handicap  to  the  next. 

Treatment.  —  Treatment  of  hookworm  disease  consists,  pri- 
marily, of  the  administration  of  a  drug  which  will  kill  and  expel 
the  worms  from  the  intestine.  In  severe  cases  this  is  followed 
by  treatment  with  a  tonic  to  bring  back  some  of  the  lost  health 
and  vitality.  Recently  it  has  been  shown  possible  to  hasten 
recovery  after  expulsion  of  the  worms  by  vaccinations  prepared 
from  bacteria  which  are  found  in  abundance  in  the  faeces.  This 
indicates  that  some  of  the  evil  effects  of  hookworm  disease  are 
due  to  absorption  of  bacterial  toxins  through  the  injured  intestine. 

Until  recently  the  classical  remedy  for  use  against  hookworm 
has  been  thymol.  This  is  a  drug  which  is  poisonous  to  the 
human  system  but  under  ordinary  circumstances  is  not  absorbed 
by  the  digestive  tract.  It  is,  however,  very  soluble  in  alcohol, 
ether  and  various  oils,  so  that  certain  precautions  have  to  be 
taken  in  its  use,  and  it  should  not  be  taken  except  under  medical 
supervision.  Thymol  is  not  highly  efficient  except  in  repeated 
doses,  taken  some  days  apart,  and  this  is  a  severe  handicap  in 
its  use.  During  the  five-year  period  from  1909  to  1914,  however, 
the  American  Hookworm  Commission,  largely  by  the  cooperation 
of  local  physicians,  treated  nearly  700,000  hookworm  patients 
in  southern  United  States  with  thymol. 

A  few  years  ago  oil  of  chenopodium  came  into  favor  in  some 
parts  of  the  United  States  as  a  remedy  for  hookworm,  and  is  now 
rapidly  supplanting  all  other  remedies  in  all  parts  of  the  world. 
It  is  made  from  a  common  weed,  usually  called  Jerusalem  oak 
or  goose-foot,  and  is  therefore  very  cheap  and  the  supply  inex- 
haustible. It  is  more  effective  than  thymol  and  is  if  anything 
less  dangerous  to  the  patient.  According  to  Hall  and  Foster, 
oil  of  chenopodium  is  not  entirely  harmless,  and  among  other 
effects  is  distinctly  constipating.  To  hasten  the  elimination  of 
the  chenopodium  as  well  as  to  counteract  the  constipating  effect 


264  HOOKWORMS 

and  the  slow  absorption  through  the  intestinal  walls,  Hall  and 
Foster  strongly  advise  giving  castor  oil  with  the  chenopodium 
and  also  afterward;  this  gives  a  maximum  of  both  efficacy  and 
safety.  The  usual  method  of  giving  oil  of  chenopodium  is  five 
to  15  drops  at  two  hour  intervals;  each  dose  should  be  accom- 
panied by  castor  oil. 

A  number  of  investigators  have  pointed  out  the  superior  effect 
of  oil  of  chenopodium  when  given  with  chloroform.  Hall  and 
Foster,  by  means  of  extensive  experiments  on  dogs,  have  demon- 
strated that  chloroform  itself  is  more  efficient  against  hookworms 
than  any  other  drug  with  which  they  have  experimented,  and  they 
could  find  no  evidence  of  superior  efficiency  of  a  combined  use 
of  both  drugs,  except  in  case  of  accompanying  infection  with 
Ascaris,  against  which  oil  of  chenopodium  is  particularly  effec- 
tive. Chloroform  dissolved  in  castor  oil  can  be  given  internally 
in  from  three  to  four  gram  doses  with  as  great  a  degree  of  safety 
as  can  other  drugs  in  common  use  for  worms,  its  safety  lying  in 
its  rapid  elimination  from  the  system.  A  dose  of  chloroform 
should  not  be  repeated,  however,  in  less  than  three  weeks,  since  it 
does  some  temporary  damage  to  the  liver  which  may  not  be 
completely  repaired  in  less  than  that  time. 

Beta-naphthol  is  considered  by  some  physicians  better  than 
thymol,  especially  when  distributed  to  laborers  for  use  without 
medical  supervision,  since  there  is  less  chance  of  bad  results,  and 
it  can  be  taken  safely  by  an  ignorant  person  with  a  few  simple 
directions.  This  drug  is  used  for  treatment  of  coolie  laborers 
in  Ceylon,  and  new  consignments  of  coolies  are  treated  with  it 
whether  infected  or  not,  since  a  great  majority  of  them  are 
parasitized. 

Male  fern  is  sometimes  used  for  expelling  hookworms  but  is 
more  dangerous  than  either  thymol  or  beta-naphthol,  is  more 
expensive  and  is  if  anything  less  efficacious.  Oil  of  eucalyptus 
has  also  been  used  with  some  success.  It  has  the  advantage  of 
being  less  unpleasant  and  less  dangerous  than  some  of  the  other 
drugs  in  common  use. 

Prevention.  —  Methods  of  prevention  of  hookworm  disease 
are  suggested  by  the  mode  of  infection,  namely,  contact  with 
soil  or  water  contaminated  by  infected  faeces.  The  ways  in 
which  such  contact  may  be  made  are  numerous,  and  vary  with 
the  habits,  occupation  and  wealth  of  the  inhabitants.      Plan- 


PREVENTION  265 

tation  workers  on  our  sugar  and  cotton  plantations  and  on  the 
coffee  plantations  of  Central  and  South  America,  and  the  coolies 
working  on  the  estates  of  China,  India  and  other  tropical  coun- 
tries, practically  never  wear  shoes.  The  necessity  for  shoes  is 
unknown,  the  discomfort  of  using  them  when  the  habit  of  going 
without  them  has  been  long  established  makes  their  use  difficult 
to  encourage,  and  there  are  very  few  who  could  afford  such 
luxuries  even  if  their  value  were  appreciated.  As  shown  above, 
the  hookworm  larva?  in  soil  or  water  commonly  gain  access  to  their 
hosts  through  bare  feet.  The  readiness  with  which  infection  may 
occur  by  contact  with  contaminated  ground  or  water  is  shown  by 
the  case  of  a  prominent  American  in  Porto  Rico  who  became 
infected  by  removing  his  boots  and  wading  in  a  small  pool. 
Kneeling  bare-kneed  or  resting  the  bare  hands  on  the  moist 
ground  beside  a  stream  or  pool  to  drink;  drinking  water  which 
has  been  directly  or  indirectly  polluted;  dirt-eating,  which  is  a 
common  perversion  of  the  appetite  in  intestinally  diseased  people; 
eating  with  soiled  or  dirty  hands;  the  chewing  of  dirty  finger- 
nails; in  all  these  and  a  hundred  other  ways  the  agricultural 
laborer  may  become  infected. 

Miners,  working  underground  where  they  are  continually  in 
contact  with  earth,  are  exposed  equally  as  much  as  agricultural 
laborers,  and  more  so  in  relatively  cold  countries  such  as  those  of 
central  Europe,  since  the  warmth  resulting  from  subterranean 
location  allows  the  parasites  to  thrive  where  on  the  surface  they 
would  perish.  Dirty  hands,  unsanitary  habits  and  polluted 
water  are  the  cause  of  the  high  percentage  of  hookworm  infection 
in  mines  where  no  special  preventive  measures  are  practiced. 

Sanitation.  —  Prevention  of  hookworm  disease,  were  it  not 
for  the  inevitable  ignorance  and  stupidity  of  many  of  the  people 
to  be  dealt  with,  would  be  a  relatively  easy  matter.  The  com- 
parative ease  with  which  infections  can  be  discovered,  the  read- 
iness with  which  the  parasites,  once  discovered,  can  be  expelled, 
and  the  ease  with  which  heavy  infection,  even  in  badly  infested 
countries,  can  be  prevented  by  cleanliness,  sanitation  and  care 
of  exposed  parts  of  the  body  are  factors  which  should  make  the 
hookworm  relatively  easy  prey  for  the  hygienic  reformer.  But 
the  hookworm  has  a  valiant  ally  in  the  stunted  brain  and  will  of 
its  victim  and  in  the  unsanitary  habits,  established  by  countless 
generations,  which  characterize  the  natives  of  almost  every  hook- 


266  HOOKWORMS 

worm-infested  country,  and  for  these  reasons  alone  the  eradi- 
cation of  the  disease  has  in  many  cases  been  a  greater  stumbling 
block  to  medical  science  than  that  of  even  malaria  or  yellow  fever. 
Mosquitoes  are  easier  to  control  than  are  the  hopelessly  ignorant 
and  stupid  victims  of  hookworm  disease! 

The  keynote  in  the  prevention  and  eradication  of  hookworm 
disease  is  the  prevention  of  pollution  of  the  soil,  in  other  words, 
proper  sanitation.  Not  only  the  hookworm,  but  almost  all  of  the 
true  nematode  parasites  of  the  human  intestine,  are  the  direct 
outcome  of  unsanitary  conditions.  The  early  stages  of  develop- 
ment, so  far  as  is  known,  are  invariably  passed  in  water  or  moist 
soil,  and  for  this  reason  the  sanitary  disposal  of  faeces  would 
forever  put  an  end  to  such  of  these  parasites  as  are  peculiar  to 
man.  The  difficulties  involved  in  this  simple  hygienic  principle 
are  infinitely  greater  than  the  average  civilized  and  cultured 
person  would  suspect.  In  southern  United  States,  68  per  cent 
of  the  rural  homes  are  estimated  to  be  without  privies  of  any  kind. 
In  many  rural  districts  where  privies  do  exist,  their  use  is  restricted 
to  the  women  and  children  or  to  the  family  of  the  manager. 
In  most  tropical  countries  where  coolie  laborers  are  employed, 
practically  all  of  whom  carry  infection,  no  attempt  is  made  to 
provide  any  kind  of  place  for  defecation,  not  even  a  simple  hole  in 
the  ground.  The  condition  in  this  regard  among  the  "  jibaros  " 
or  plantation  laborers  of  Porto  Rico,  for  instance,  is  fairly  repre- 
sented by  this  case  —  of  61  hookworm  patients  at  Utuado,  55 
never  had  used  privies  of  any  kind,  and  of  the  six  who  did  oc- 
casionally use  them  only  two  lived  in  rural  districts!  The  ex- 
tent to  which  the  unhygienic  conditions  may  go,  and  the  readi- 
ness with  which  infection  with  various  intestinal  worms  may  take 
place,  is  demonstrated  by  the  occurrence  in  Brazil  of  three  species 
of  intestinal  worms  in  a  baby  three  months  old. 

The  time  when  the  value  accruing  from  proper  sanitation  will 
be  realized  to  an  extent  sufficient  to  make  man  as  careful  con- 
cerning his  personal  habits  as  are  some  of  his  domestic  animals  is 
still  in  the  future;  but  it  is  reasonable  to  hope  that  it  will  soon 
be  at  hand.  It  is  a  significant  fact  that  the  domestic  cat,  which 
sanitarily  covers  up  its  excreta,  has,  on  the  average,  fewer  intesti- 
nal parasites  than  the  less  careful  dog.  Dr.  Stiles  has  recently 
tested  the  effect  of  sanitation  and  consequent  reduction  of  in- 
testinal parasites,  both  protozoans  and  worms,  by  examination  of 


PREVENTION  267 

school  children  from  sewered  houses  and  from  houses  with  privies. 
The  statistics  compiled  from  the  data  obtained  showed  that  the 
children  from  sewered  houses  possessed  fewer  parasites  and  aver- 
aged a  higher  grade  in  school  than  those  from  houses  with  privies, 
even  though  the  difference  was  undoubtedly  reduced  by  the  fact 
that  sewered  homes  suffered  from  proximity  to  the  privies  of 
unsewered  homes  and  from  consequent  infection  by  flies  and  other 
agents  of  transmission. 

The  most  important  and  effective  preventive  measure  against 
hookworm  and  other  intestinal  nematodes  which  can  be  inaugu- 
rated is  the  enforcement  of  the  building  of  privies  or  latrines 
of  some  sort,  if  it  be  only  a  ditch  which  is  occasionally  covered 
with  earth  or  disinfected,  for  the  use  of  laborers  on  plantations 
and  estates,  and  the  placing  of  a  penalty  or  fine  for  unnecessary 
pollution  of  the  ground  or  water  where  there  is  any  danger  of 
spreading  hookworm  infection,  especially  along  roads  or  on  plan- 
tations. Naturally  such  practices  as  the  use  of  night-soil  (human 
faeces)  for  manure,  which  is  extensively  practiced  in  China,  should 
be  stringently  forbidden,  unless  the  material  can  be  disinfected 
by  chemical  treatment,  as  suggested  by  Leiper.  The  faeces  of  all 
infected  persons,  as  well  as  those  of  any  suspected  persons,  should 
be  carefully  disinfected.  The  use  of  common  salt  as  a  disinfect- 
ant against  hookworm  has  been  found  efficacious,  but  it  must  be 
used  in  rather  large  quantities.  Nicoll,  in  Australia,  in  experi- 
ments recently  conducted  with  hookworms,  obtained  rather  un- 
satisfactory results  with  salt  treatment  of  infected  faeces,  unless 
the  salt  was  used  in  very  large  quantities  and  was  very  thoroughly 
mixed  with  the  infective  material.  The  spraying  of  the  earth 
walls  and  floors  of  mines  with  a  strong  salt  solution  or  other 
disinfectant,  and  a  similar  treatment  of  factories,  yards,  etc., 
which  are  known  to  be  infected,  is  a  preventive  measure  which 
is  said  to  bring  good  results,  but  in  the  light  of  Nicoll' s  experi- 
ments this  should  be  reinvestigated.  Wearing  of  boots  or  shoes 
by  mine  workers,  agricultural  laborers  and  all  who  work  with 
brick,  pottery,  earth  roofing,  etc.,  is  recommended  as  a  protective 
measure  by  the  boards  of  health  in  some  countries.  This  cer- 
tainly is  a  good  recommendation  when  it  can  be  followed,  but  it 
should  be  remembered  that  many  who  need  protection  the  most 
are  unable  to  invest  in  such  luxuries  as  shoes,  and  that  at  best 
little  advance  towards  the  final   eradication  of  the   disease  is 


268  HOOKWORMS 

made  by  such  measures.  •  If  money  sufficient  to  buy  shoes  and 
other  protective  garments  were  invested  in  improving  sanitary 
conditions  much  more  permanent  good  would  result.  This  does 
not  mean,  however,  that  such  protection  as  is  gained  by  the  use 
of  shoes  and  spraying  of  ground  is  not  well  worth  while  for  such 
individuals  as  can  afford  it  and  who  are  forced  by  occupation  or 
other  circumstances  to  come  in  contact  with  polluted  soil. 

The  isolation  and  treatment  of  infected  persons  is  to  be  highly 
recommended,  especially  in  case  of  immigrants  or  new  arrivals 
from  infected  regions.  In  1910  the  Board  of  Health  of  San  Fran- 
cisco made  an  examination  of  a  shipload  of  Hindus  which  had 
just  arrived  and  found  90  per  cent  to  be  infected,  whereupon  a 
quarantine  was  established,  and  has  since  been  maintained,  for 
hookworm  patients.  Every  colony  of  Hindu  coolies  in  California 
is  a  center  from  which  hookworm  disease  is  spreading.  Had  a 
hookworm  quarantine  been  established  years  before,  California 
would  have  been  to  a  great  extent  free  from  this  parasite.  Quar- 
antine measures  have  been  taken  in  Natal,  where  all  infected 
immigrants  are  treated  before  being  assigned  to  plantations. 
When  the  infection  does  appear  in  a  mine  or  plantation  the  in- 
fected persons  should  be  treated,  and  not  allowed  to  return  to 
work  until  their  faeces  are  free  from  eggs. 

The  treatment  of  hookworm  disease  is  of  such  vital  importance 
to  the  public  of  any  endemic  region  that  it  should  be  supervised 
and  aided  by  the  government.  Such  aid  should  consist  in  the 
establishment  of  free  dispensaries  for  hookworm  patients,  the 
supply  of  necessary  drugs  at  cost  for  the  treatment  of  hookworm 
disease,  the  appointment  of  inspectors  to  enforce  sanitary  regu- 
lations, and  the  distribution  of  information  regarding  the  disease 
by  free  pamphlets,  pubHc  lectures  and  school  instruction.  In 
the  United  States  this  work  has  been  done  largely  by  the  American 
Hookworm  Commission,  financed  by  a  gift  of  11,000,000  from 
John  D.  Rockefeller.  In  1914  the  Rockefeller  Foundation  ex- 
tended the  work  of  hookworm  eradication  "  to  those  countries  and 
peoples  where  conditions  invite."  Such  work  has  been  begun  in 
a  number  of  West  Indian  islands.  Central  America  and  Egypt. 

It  has  been  pointed  out  that  demonstration  as  well  as  instruc- 
tion is  necessary  to  impress  the  natives  of  hookworm  districts 
with  the  advantages  of  sanitation  and  hygienic  conditions.  It 
is  absurd  to  rely  upon  the  ability  of  the  average  native,  dwelling 


SANITATION  269 

in  a  filthy  environment  in  which  he  was  born  and  brought  up,  to 
form  a  conception  of  community  cleanUness,  which  he  has  never 
seen,  resulting  in  public  benefits  which  he  has  never  known.  The 
erection  of  schools,  hospitals,  residence  sections,  etc.,  which  are 
models  of  simple  but  efficient  sanitation,  would  go  much  further 
toward  securing  the  cooperation  of  natives  in  duplicating  such 
conditions  than  would  any  amount  of  instruction  without  such 
practical  demonstrations. 


CHAPTER  XV 
OTHER  INTESTINAL  ROUNDWORMS 

General  Account.  —  As  compared  with  the  hookworms  all  the 
other  intestinal  roundworms,  except  trichina,  which  will  be  dis- 
cussed in  the  following  chapter,  sink  into  relative  insignificance, 
but  there  are  several  species  which  are  very  common  in  some  parts 
of  the  world  and  some  which  are  of  very  wide  distribution.  The 
pathological  effects  of  some  of  these  worms  appear  to  be  slight 
or  almost  entirely  negligible,  —  while  others,  at  least  in  individual 
cases,  cause  severe  symptoms  and  may  even  be  a  direct  cause 
of  death.  Recently,  as  has  been  remarked  in  a  preceding  chap- 
ter, more  and  more  suspicion  is  being  aroused  against  various 
intestinal  worms,  especially  those  which  habitually  inhabit  the 
ccecum  and  appendix,  as  playing  a  leading  part  in  producing 
appendicitis.  The  relation  of  intestinal  worms  to  bacterial  in- 
fections is  discussed  on  pp.  203-204. 

As  regards  the  selection  of  a  drug  for  treatment  of  any  of 
these  rarer  intestinal  parasites,  certain  general  principles  should 
be  of  value.  As  has  been  pointed  out  by  Hall  and  Foster, 
"  almost  all  anthelmintics  {i.e.,  drugs  used  against  worms)  are 
poisons,  intended  to  kill  or  stupefy  or  otherwise  disable  and  re- 
move worms,  while  at  the  same  time  inflicting  a  minimum  amount 
of  damage  on  the  host  animal  by  virtue  of  the  comparative 
insolubility  of  the  drugs  or  their  rapid  elimination."  For  worms 
situated  in  the  upper  portions  of  the  digestive  tract,  drugs  such 
as  chloroform,  which  are  rapidly  absorbed  and  eliminated,  can 
be  used,  whereas  for  worms  situated  in  the  lower  portions  of 
the  digestive  tract,  insoluble  drugs  would  in  general  be  better. 
That  certain  drugs  have  more  or  less  specific  action  against 
certain  species  of  worms  is  true,  as  evidenced  by  the  case  of  oil 
of  chenopodium  against  ascarids,  and  chloroform  against  hook- 
worm. It  is  quite  probable,  however,  that  this  apparently  spe- 
cific action  may  be  due  rather  to  a  mode  of  life  of  the  worm 
affected  which  makes  it  particularly  easily  reached  by  the  drug. 
Hall  and  Foster,  for  instance,  suggest  that  the  striking  efficiency 

270 


INTESTINAL  NEMATODES 


271 


Fig.  106.  Intestinal  nematodes  of  man,  natural  size.  Male  and  female  of  each 
species  shown,  except  Strongyloides,  in  which  only  the  females  is  known.  The 
female  of  (Esophagostoma  is  immature,  the  mature  form  being  unknown. 


272  OTHER  INTESTINAL  ROUNDWORMS 

of  chloroform  against  hookworms  may  be  due  to  the  fact  that 
hookworms  are  blood-suckers  and  that  the  chloroform  rapidly 
absorbed  by  the  blood  is  ingested  by  the  hookworms  in  amounts 
sufficient  to  cause  stupefaction  or  death. 

The  presence  of  intestinal  worms  of  most  species  can  be  de- 
termined by  the  finding  of  the  eggs  in  the  faeces,  and  in  most  cases 
the  eggs  are  characteristic  enough  to  make  a  determination  of 
the  species  fairly  easy.  It  often  facilitates  the  search  for  para- 
site eggs  to  concentrate  them  in  the  following  manner:  Mix  a 
portion  of  the  faeces  the  size  of  a  walnut  with  60  cc.  of  distilled 
water,  strain  through  several  thicknesses  of  wide-mesh  surgical 
gauze  and  centrifuge  at  high  speed  for  about  ten  seconds.  Pour 
off  most  of  the  liquid,  add  more  water,  shake  thoroughly  and 
centrifuge  again.  The  material  thrown  to  the  bottom  of  the 
tube  contains  the  eggs,  which  can  readily  be  found  under  a  micro- 
scoper  A  bit  of  the  centrifuged  material  is  placed  on  a  slide  with 
a  little  distilled  water.  In  two  or  three  minutes  the  eggs  will 
settle  on  the  slide,  and  the  excess  liquid  can  be  poured  off.  The 
eggs  of  parasitic  worms  vary  in  size,  shape,  color,  surface  mark- 
ings and  state  of  development.  Most  eggs  are  colored  yellow 
or  brown  from  bile  in  the  faeces  but  the  eggs  of  the  hookworms, 
Strongyloides,  and  a  few  others  remain  clear  and  colorless.  The 
characteristics  of  the  eggs  of  the  commoner  parasitic  worms  are 
shown  in  a  comparative  way  in  Fig.  61,  p.  205.  In  the  case  of  a 
few  intestinal  nematodes  eggs  do  not  appear  in  the  faeces.  In 
the  pinworms,  for  instance,  the  adult  female  containing  the  eggs 
usually  passes  out  entire,  whereas  in  Strongyloides  the  eggs  hatch 
before  leaving  the  host. 

Preventive  measures  against  practically  all  of  the  true  nema- 
tode parasites  of  the  intestine  consist  mainly  in  proper  sanitation, 
a  discussion  of  which  will  be  found  on  p.  265.  It  is  possible  that 
some  of  the  intestinal  nematodes  may  occasionally,  at  least, 
utilize  an  intermediate  host  of  some  kind,  but  even  if  this  were 
true  sanitary  disposal  of  human  faeces  would,  as  said  before,  be 
sufficient  to  exterminate  such  parasites  as  are  peculiar  to  man. 
The  nematodes  which  occur  in  other  animals  as  well  as  man  have 
to  be  guarded  against  by  other  means  also.  The  spiny-headed 
worms,  which  are  transmitted  in  the  bodies  of  insects  which 
serve  as  intermediate  hosts,  are,  of  course,  subject  to  quite  dif- 
ferent prophylactic  measures. 


ASCARIS  273 

Ascaris  or  Eelworm.  —  Of  greatest  importance  of  these  lesser 
intestinal  parasites  is  the  eelworm,  Ascaris  lumbricoides  (Fig. 
106).  Ascaris  is  one  of  the  largest  nematode  parasites  known^ 
the  female  averaging  about  ten  inches  in  length,  and  occasion- 
ally measuring  a  foot  and  a  half,  while  in  diameter  the  body  is 
about  as  large  as  an  ordinary  lead  pencil.  The  males  are  usually 
several  inches  shorter.  These  worms  are  among  the  most  fre- 
quent human  parasites.  They  occur  in  all  parts  of  the  world 
and  are  found,  especially  in  children,  in  the  majority  of  temperate 
countries,  even  in  countries  as  far  north  as  Greenland  and  Fin- 
land. In  the  tropics  they  are  abundant  and  are  almost  univer- 
sally present  in  children,  each  individual  harboring  anywhere 
from  two  or  three  to  several  hundred  worms. 

Ascaris  can  be  recognized  immediately  by  its  large  size  and 
robust  form.     The  males  (Fig.  107)  can  be  distinguished  by  the 


Fig.  107.  Ascaris,  dissected  to  show  anatomy;  female  above,  male  below. 
Note  ribbon-like  intestine  (cross-barred)  with  pharynx  at  its  anterior  end;  the 
coiled  threadlike  ovaries  in  female  and  testis  in  male;  the  large  kinky  oviducts  in 
the  female,  uniting  to  form  a  vagina  near  the  external  opening  on  the  anterior  third 
of  the  body;  and  in  the  male  the  large  sperm  duct  opening  at  the  ventrally-curved 
posterior  end  of  the  body  in  common  with  the  intestine. 

sharp  downward  curve  of  the  posterior  end  of  the  body,  the  female 
(Fig.  107)  having  a  straight  and  rather  stumpy  tail.  Both 
sexes  are  more  slender  at  the  head  than  at  the  tail  end.  The 
sexual  organs  occupy  the  greater  part  of  the  body.  In  the  female 
they  consist  of  two  coiled  threadlike  ovaries  (Fig.  107)  and  a  pair 
of  large  oviducts  in  the  form  of  kinky  tubes  which  open  about 
one-third  of  the  way  back  from  the  anterior  end.  In  the  male 
there  is  a  single  coiled  threadlike  testis  and  a  single  sperm  duct 
(Fig.  107),  the  latter  opening  at  a  cloaca  at  the  posterior  end  of 
the  body.  The  size  and  simplicity  of  the  organs  makes  Ascaris 
a  favorite  subject  for  class-room  dissection.     The  human  species, 


274  OTHER  INTESTINAL  ROUNDWORMS 

Ascaris  lumbricoides,  is  now  usually  looked  upon  as  a  variety 
of  the  species  which  occurs  in  hogs  in  almost  every  country  in 
the  world,  and  which  is  sometimes  known  as  A.  suilla. 

The  life  history  of  Ascaris  is  usually  thought  to  be  very 
simple.  The  eggs,  of  which  thousands  are  deposited  by  a  single 
female,  develop  within  the  eggshell  outside  of  the  human  body, 
in  water,  soil  or  manure  piles,  wherever  the  proper  conditions  of 
temperature  can  be  found.  The  eggs  (Fig.  108)  are  about  0.06  mm. 
long  by  0.04  mm.  wide  (;f^(y  by  ^^(^  of  an  inch),  elliptical  in  form 

with  a  thick  transparent  shell, 
usually  bile  -  stained,  covered 
over  outside  by  irregular  albu- 
minous coats  which  give  them 
a  rough  warty  appearance. 
When  passed  from  the  diges- 
o  tive  tract  no  sign  of  segmen- 
Fi:   108.    Egg  of  Asmns;^,  surface   tation     can     be     Seen.     Under 

view    showing    warty    albununous    coat;  . 

B,  same  in  "optical   section,"  i.e.,  with  lavorable     conditions     ot     Optl- 

microscope  focused  on  center  of  egg  in-  ^^^  temperature  (33°  C), 
stead  of  on  surface.  . 

moisture,  and  oxygen  supply 
the  eggs  develop  in  from  10  days  to  a  month,  but  may  be  retarded 
for  a  long  time  by  low  temperatures,  excessive  dryness  or  in- 
sufficient oxygen.  Although  continued  dryness  at  high  tem- 
perature may  be  fatal  to  the  eggs,  yet  under  natural  conditions 
in  soil  there  is  probably  almost  always  sufficient  moisture  to 
allow  development  to  proceed,  and  the  developed  eggs  may  live 
for  several  years.  The  eggs  are  extremely  resistant  to  most 
chemical  reagents,  even  when  used  in  very  strong  dilutions,  so 
that  ordinary  methods  of  disinfection  would  be  of  little  value  in 
destroying  them.  The  use  of  human  faeces  (night  soil)  as  a  fer- 
tilizer undoubtedly  results  in  wholesale  contamination  of  vege- 
tables and  other  garden  products. 

The  eggs  only  rarely  hatch  outside  of  the  body;  ordinarily 
the  larvae  escape  only  after  the  eggs  have  been  ingested  and  have 
reached  the  small  intestine.  Since  eggs  injected  under  Ixie  skin 
will  hatch  it  is  evident  that  some  other  factor  besides  the  digestive 
juices  is  influential  in  liberating  the  larvae. 

Stewart,  in  recent  experiments  in  China,  was  the  first  to  dem- 
onstrate that  Ascaris  might  not  develop  directly  in  the  intestine 
of  its  host.  Subsequent  experiments  by  Stewart  and  also  by 
Ransom  and  Foster  have  fully  corroborated  Stewart's  work. 


LIFE  HISTORY  OF  ASCARIS  275 

Ripe  eggs  ingested  by  rats  and  other  rodents  hatch  in  the 
small  intestine.     Some  of  the  newly-hatched  larvae  may  be  elimi- 
nated in  the  faeces,  but  others  penetrate  the  wall  oi  the  intestine 
and  go  to  the  liver  and  lungs 
and  occasionally  other  organs, 
including  the  abdominal  cavity. 
The  newly-hatched  larvae  mea- 
sure between  0.2  and  0.3  mm. 
in    length,    but    during   their 
migrations  and  during  their  so- 

journ  in  the  lungs  they  grow        W^         jB    /\  y^  q 

rapidly,  reaching  a  length  of 
from  1  to  1.5  mm.  by  the  tenth 
day,  when  ready  to  leave  the   ,  ^^«:    ^^^i    ^P^r^^'P/^^'^,^^^   ^*^,^T   ""^ 

^  r       V       Ascaris;  a,  freshly  hatched  larva;   o,  larva 

lungs.      They    may    reach    the   from  lung  of  rat  on  tenth  day  after  infec- 

liver  as  early  as  two  days  after  *^o"-     x  ^^^\  (Adapted  from  Stewart.) 
infection,  and  the  lungs  on  the 

third  day.  From  the  sixth  to  the  tenth  days  the  larvae  pass  from 
the  blood-vessels  into  the  air  sacs  and  bronchial  tubes  of  the  lungs, 
and  thence  through  the  trachea  to  the  mouth.  Some  larvae 
escape  from  the  mouth,  but  the  majority  are  swallowed  and  pass 
out  with  the  faeces  apparently  dead,  the  host  becoming  free  from 
parasites  in  about  two  weeks.  It  is  not  probable  that,  as  at  first 
suggested  by  Stewart,  the  rat  normally  acts  as  an  intermediate 
host,  but  rather  the  development  of  Ascaris  to  the  lung  stage  and 
failure  to  complete  the  development  in  the  intestine  may  be  con- 
sidered as  a  case  of  imperfect  adaptability  of  the  worm  to  this 
host.  It  was  subsequently  shown  by  Stewart  himself  and  also  by 
Ransom  and  Foster  that  a  similar  development  in  the  lungs  takes 
place  in  pigs  and  other  animals  as  well  as  in  rats,  and  it  is  rea- 
sonable to  suppose  that  a  direct  development  in  a  single  host 
normally  takes  place.  However,  this  has  been  shown  to  be  uhe 
case  only  in  a  few  instances,  and  in  cases  where  a  massive  infec- 
tion would  be  expected  from  feeding  enormous  numbers  of  eggs  to 
susceptible  animals  only  a  small  number  of  Ascaris  developed, 
and  in  some  instances  none  at  all. 

Both  in  the  hog  and  in  man,  susceptibility  to  Ascaris  infection 
decreases  with  age.  The  higher  rate  of  infection  in  children  is 
probably,  however,  due  to  careless  habits  as  well  as  to  greater  sus- 
ceptibility. 


276 


OTHER  INTESTINAL  ROUNDWORMS 


The  symptoms  produced  by  Ascaris  infection  vary  greatly 
with  different  individuals.  In  some  cases  a  great  number  of 
Ascaris  may  be  harbored  with  practically  no  ill  effects.  Often, 
however,  even  when  small  numbers  are  present,  peculiar  mental 
and  constitutional  ailments  occur,  such  as  feverishness,  anemia, 
restlessness,  epilepsy,  insomnia  and  deliriousness.  In  combina- 
tion with  these  nervous  troubles  there  is  usually  some  dyspeptic 
trouble,  such  as  irregular  appetite,  nausea  and  stomach  aches. 
The  nervous  and  other  constitutional  symptoms  are  the  result 

of  poisoning  or  intoxication  from  sub- 
stances given  off  by  the  worms  in  the 
intestine,  as  explained  in  Chapter  XI, 
p.  203.  The  worms  occasionally  creep 
forward  into  the  throat  or  nose.  Their 
wandering  into  other  organs  through 
ducts  leading  from  the  intestine  or 
into  the  body  cavity  through  the  in- 
testinal walls  often  gives  rise  to  serious 
abscesses  which  call  for  an  operation 
and  removal  of  the  intruders.  The 
production  of  a  serious  and  often 
fatal  pneumonia  in  rats,  pigs  and  other 
animals  by  larvae  developed  from  eggs 
experimentally  fed  to  them  leaves 
little  room  for  doubt  but  that  a  sim- 
FiG.  110.    Human  whipworm,  ji^r  Condition  is  produced  after  human 

Trichuris    trichiura:    A,    female;    .    »      ^.  ^     ,^     ,       a  •  i 

ov.,  ovary;  ut.,  uterus;  v.,  vulva;  mfcction,   and   that   Ascavis  may  be 
int.,  intestine;  w.,  whiplike  an-  the  cause  of  Certain  lung  troubles  in 

terior  end  containing  oesophagus.  . 

X  3.      B,  egg;  note  barrel  shape   numau  beingS. 

and   pluglike   bodies   at  ends.       Santonin    has    been    the    classical 

drug  for  expelling  Ascaris,  but  oil 
of  chenopodium  has  recently  been  demonstrated  to  be  considerably 
more  effective.  According  to  Hall  and  Foster  oil  of  chenopodium, 
properly  administered  (see  Chap.  XIV,  p.  264),  is  almost  100 
per  cent  effective  for  ascarids,  and  is  more  dependable  than  any 
other  drug  commonly  used  for  worms. 

Whipworm.  With  the  possible  exception  of  the  hookworms 
and  Ascaris  J  the  whipworm,  Trichuris  trichiura  (Figs.  106  and 
110),  is  the  most  common  worm  parasitic  in  man.     It  is  a  nema- 


WHIPWORM  277 

testine  occupy  the  thicker  posterior  part  of  the  body.  The  fe- 
male whipworms,  which  are  always  far  more  numerous  than  the 
males,  are  about  two  inches  long,  while  the  males  are  a  little 
smaller. 

The  human  whipworm  is  found  in  almost  every  part  of  the 
world,  but  is  especially  prevalent  in  warm  countries;  it  para- 
sitizes both  man  and  monkeys.  It  usually  makes  its  home  in 
the  coecum  but  occasionally  establishes  itself  in  the  appendix 
or  large  intestine.  It  is  usually  said  to  transfix  the  wall  of  the 
coecum  with  its  threadlike  anterior  portion,  but  there  is  some  evi- 
dence to  show  that  it  merely  buries  its  long  head  and  "  neck  " 
between  the  folds  of  the  intestinal  wall. 

Usually  the  only  evidence  of  the  presence  of  whipworms  is 
the  appearance  of  the  characteristic  dark-colored,  barrel-shaped 
eggs  (Fig.  HOB)  in  the  faeces.  These  eggs,  like  those  of  Ascaris, 
develop  in  water  or  moist  soil.  The  embryo-containing  eggs  are 
very  resistant  to  adverse  conditions  and  may  live  for  years 
without  losing  their  vitality.  Infection,  as  far  as  known,  occurs 
as  in  the  case  of  Ascaris.  The  worms  may  attain  maturity 
and  produce  eggs  in  less  than  a  month  after  the  eggs  have  been 
swallowed.  Although  the  whipworm  feeds  on  blood  to  some 
extent,  and  undoubtedly  produces  toxins,  as  evidenced  by  the 
increase  in  eosinophiles  (see  p.  203)  in  the  blood  which  nearly 
always  occurs  in  case  of  whipworm  infection  and  by  the  occa- 
sional mental  disturbances  and  other  nervous  symptoms,  this 
worm  usually  produces  very  slight,  in  fact  often  unnoticeable, 
effects.  It  is,  however,  thought  by  some  workers  to  be  one  of 
the  intestinal  parasites  most  frequently  involved  in  causing 
appendicitis.  It  is  very  difficult  to  dislodge  the  whipworm  by 
the  usual  methods  used  for  expelling  intestinal  parasites,  prob- 
ably due  to  its  very  firm  attachment  by  the  long  slender  "  neck." 
Oil  of  chenopodium  administered  as  for  hookworm  (see  p.  264) 
is  probably  the  most  effective  remedy. 

Pinworm.  —  One  of  the  most  frequent  and  widely  distributed 
intestinal  parasites  of  man  is  the  pinworm,  Oxyuris  vermicularis 
(Figs.  106  and  111).  This  parasite  occurs  almost  universally  in 
children  at  one  time  or  another  in  temperate  as  well  as  tropical 
countries;  it  inhabits  the  lower  part  of  the  small  intestine  and 
the  coecum. 

The  adult  females  (Fig.  Ill  9  )  are  whitish  worms  about  two- 


278 


OTHER  INTESTINAL  ROUNDWORMS 


fifths  of  an  inch  in  length,  and  have  about  the  diameter  of  an 
ordinary  pin.  The  males  (Fig.  111<J)  are  only  about  half  as 
large  and  have  the  posterior  end  of  the  body  rolled  ventrally. 
The  adult  females  filled  with  eggs  leave 
the  small  intestine  and  coecum  and  wander 
back  to  the  rectum  whence  they  are 
passed  out  with  the  faeces  or  creep  out 
of  the  anus,  especially  in  the  evening 
or  at  night,  causing  intense  itching. 
These  egg-filled  females,  or  the  free  eggs 
which  already  contain  coiled  embryos, 
live  in  the  moist  groove  between  the 
buttocks,  in  girls  sometimes  creeping  for- 
ward to  the  vagina.  From  the  scratching 
and  rubbing  which  results  from  the  itch- 
ing in  the  vicinity  of  the  anus  the  fingers 
and  fingernails  become  infected  with  the 
eggs.  The  eggs  may  then  be  transferred 
to  the  mouth  directly  or  indirectly,  thus 
causing  reinfection,  or  they  may  be  trans- 
mitted from  person  to  person  by  unclean 
hands.  Infection  may  also  occur  by 
swallowing   the  mature  egg-filled  female 

o!^r^lJ^^9:  ^°™^'  •''•  by  ^^^  ^^^^^  °f  '^^  vegetables 
female;     $,    male;     ph.,  or  other  foods  which  have  been  polluted 

^vX^;  ir'/utems-t!;  by  the  eggs.  As  in  the  case  of  other 
anus;  v.,  vulva;  t.,  testis;  parasite  eggs,  those  of  the  pinworm  may 
(Aftet-ciTuTfrom''Brau„'-  ^Iso  be  Scattered  by  flies  which  have 
visited  infected  faeces. 

When  first  deposited,  the  eggs,  often  hanging  together  like 
short  strings  of  beads,  contain  larvae  which  resemble  tadpoles 
(Fig.  11 2 A).  In  the  faeces  or  in  the  moist  groove  between  the 
buttocks  the  larvae,  still  in  the  eggs,  transform  within  a  few  hours 
into  worms  of  typical  nematode  form  (Fig.  112B).  Later  stages 
are  shown  in  Figs.  112C  and  D. 

After  infection,  which  probably  nearly  always  occurs  by  way 
of  the  mouth,  about  two  or  three  weeks  elapse  before  sexual 
maturity  is  again  attained  and  the  eggs  and  females  reappear 
in  the  faeces. 

While  usually  no  inconvenience  is  felt  from  the  presence  of 


STRONGYLOIDES 


279 


even  large  numbers  of  pinworms,  since  they  do  not  suck  blood 
and  seldom  cause  intestinal  lesions,  yet  they  sometimes  produce 
reflex  nervous  symptoms,  probably  by  secretion  of  toxins,  and 
they  may  interfere  with  the  normal  action  of  the  bowels.     As 


Fig.  112.  Early  development  of  pin  worm,  Oxyuris  vermicularis.  A,  newly  laid 
egg  containing  tadpole-like  larva;  B,  egg  12  hrs.  later  with  nematode-like  larva; 
C,  egg  with  fully  developed  embryo;  D,  newly  hatched  embryo.  X  500,  (A  and 
B  after  Braun;  C  and  D  after  Leuckart.) 

remarked  elsewhere  pinworms  are  believed  to  be  sometimes, 
and  perhaps  frequently,  the  original  cause  of  lesions  in  the  ap- 
pendix which  culminate  in  appendicitis.  The  intense  itching 
which  they  produce  by  creeping  in  the  vicinity  of  the  anus  is 
usually  the  most  disagreeable  effect  of  their  presence. 

On  account  of  their  situation  in  the  lower  part  of  the  intestine, 
treatment  for  pinworms  should  be  by  drugs  which  are  not  rapidly 
absorbed  from  the  intestine  but  are  relatively  insoluble.  Thy- 
mol, male  fern  and,  best  of  all,  oil  of  chenopodium  are  effective 
remedies. 

Strongyloides,  —  Another  parasite  of  the  intestine  which  is  of 
wide  distribution  and  locally  very  common  is  Strongyloides  ster- 
coralis,  sl  very  small  worm  about  one-tenth  of  an  inch  in  length 
which  bores  deep  into  the  mucous  membrane  of  the  intestine.  The 
female  strongyloid  (Figs.  106  and  113A),  which  is  the  only 
sex  known,  can  be  recognized  by  its  small  size,  and  microscopi- 
cally by  the  chain  of  six  or  eight  eggs,  lying  near  the  middle  of 


280 


OTHER  INTESTINAL  ROUNDWORMS 


Fig.  113.  Life  history  of  Strongyloides  stercoralis.  A,  adult  female  in  intestine 
(note  long  pharynx,  egg-containing  uterus  and  vaginal  opening  on  posterior  third 
of  body;  B,  newly  born  embryo  as  passed  with  faeces;  C  and  D,  adult  female  and 
male,  respectively,  of  free-living  generation;  E,  "  rhabditiform "  larva,  from  female 
of  free-living  generation;  F,  filariform  larva,  resembling  grandparent,  and  formed 
by  metamorphosis  of  E,  ready  to  infect  by  boring  through  skin.  X  75.  (Partly 
after  Looss.) 


STRONGYLOIDES  281 

the  body,  visible  through  the  deUcate  body  wall.  The  eggs, 
which  are  deposited  deep  in  the  intestinal  coat,  normally  hatch 
before  leaving  the  digestive  tract  of  the  host  and  grow  con- 
siderably, so  that  when  the  faeces  of  an  infected  person  are  ex- 
amined microscopically  the  active  writhing  larvae  (Fig.  113B), 
250 /x  (y^^  of  an  inch)  in  length,  can  be  seen  darting  about  in 
snakelike  fashion.  Further  development  of  the  larvae  takes 
place  in  water  of  fairly  high  temperature,  such  as  would  be  found 
under  the  burning  rays  of  a  tropical  sun.  Under  such  conditions 
the  larvae  attain  a  sexually  mature  form,  male  and  female  (Fig. 
113C  and  D),  in  which  they  are  quite  different  from  their  parents. 
They  now  copulate,  and  the  females  lay  30  or .  40  eggs,  all  within 
two  days.  This  second  generation  of  eggs  hatch  into  tiny  free- 
living  larvae  (Fig.  113E)  resembling  the  parents,  but  after  their 
first  moult  they  lose  the  parental  characteristics  and  become 
like  their  grandparents  (Fig.  113F).  After  having  reached  this 
stage,  they  soon  die  unless  they  gain  entrance  to  the  digestive 
tract  of  a  human  being  again.  An  unusual  phenomenon  is 
shown  by  these  worms  in  that  the  life  cycle,  under  less  favorable 
conditions,  can  be  abridged,  and  the  alternation  of  generations 
eliminated.  If,  for  instance,  the  larvae  in  the  faeces  be  exposed 
to  the  cooler  water  of  a  temperate  country,  they  do  not  be- 
come sexually  mature  and  reproduce,  but  transform  directly 
into  the  parasitic  type  and  reinfect  without  further  repro- 
duction. 

The  method  of  infection  is  similar  to  that  of  the  hookworms. 
While  the  larvae  may  occasionally  gain  entrance  to  their  host 
with  polluted  water  or  food,  they  are  able  to  bore  through  the 
skin  as  do  the  hookworm  larvae,  and  it  is  probable  that  this  is 
the  more  usual  method. 

As  a  rule  Strongyloides  does  not  cause  very  serious  ill  effects 
from  its  pursuit  of  life  and  happiness  in  the  intestine.  Nearly 
all  cases  of  diarrhea  and  dysentery,  in  which  the  strongyloids 
were  formerly  supposed  to  be  the  chief  agent,  can  now  be  ascribed 
to  some  other  cause,  the  strongyloids  being  more  or  less  innocent 
bystanders.  Barlow,  however,  reports  that  in  23  cases  in 
Honduras,  five  of  them  uncomplicated,  such  symptoms  as  in- 
termittent diarrhea  without  blood  or  mucus  in  the  stools,  colic 
and  certain  nervous  symptoms  were  in  evidence.  In  many  cases 
where  a  diseased  condition  of  the  intestine  is  brought  about  by 


282  OTHER  INTESTINAL  ROUNDWORMS 

some  other  causes,  the  strongyloids  increase  in  number  and  un- 
doubtedly intensify  the  bad  condition. 

The  worms  are  not  so  readily  expelled  by  drugs  as  are  most  of 
the  intestinal  parasites,  being  able,  on  account  of  their  small  size, 
to  stow  themselves  away  in  the  folds  and  villi  of  the  intestine 
where  drugs  do  not  reach  them. 

Since  the  strongyloid  occurs  in  the  same  countries  as  do  the 
hookworms,  though  more  limited  in  distribution,  and  has  a 
similar  mode  of  transmission  and  infection,  the  same  preventive 
measures  which  are  used  against  hookworm  are  of  service  against 
this  comparatively  harmless  companion  of  it. 

Other  Species.  —  There  are  a  great  many  other  worms  which 
occasionally  make  their  home  in  the  human  digestive  tract,  some 
being  locally  common,  others  merely  sporadic  in  their  occurrence; 
some,  in  fact,  are  not  truly  parasites  at  all,  but  have  merely 
established  themselves  temporarily  after  having  been  swallowed 
with  infected  food.  Stephens  lists  59  species  of  nematodes  as 
having  been  observed  in  man.  None  of  those  not  already 
mentioned  can  be  considered  of  great  importance,  since  they 
seldom  cause  serious  ailments  and  are  most  of  them  rare.  Only 
those  which  are  true  parasites  and  have  been  recorded  from  man 
more  than  once  need  be  mentioned  here. 

Belonging  to  the  same  family  as  Ascaris  (Ascaridse)  or  to 
closely  allied  families  are:  Belascaris  cati  (or  Ascaris  mystax) 
(Fig.  106)  and  Toxascaris  limbata  (or  Ascaris  marginata),  small 
Ascarids  two  or  three  inches  in  length,  normally  parasitic  in  cats 
and  dogs  respectively,  found  practically  all  over  the  world  but 
only  occasionally  in  man;  and  Physaloptera  mordens  (Fig.  106), 
a  worm  one  and  a  half  to  two  inches  long,  which  appears  to  be 
not  uncommon  in  negroes  in  central  East  Africa. 

Allied  to  the  hookworms  and  having  an  expanded  umbrella- 
like "  bursa  "  at  the  posterior  end  of  the  male  are  several  species 
of  Trichostrongylus  (or  Strongylus).  T.  instabilis  (suhtilis)  (Figs. 
106  and  114)  is  a  small  worm  from  four  to  six  mm.  (one-fifth  of 
an  inch)  in  length,  somewhat  resembling  a  hookworm  but  much 
more  slender.  It  is  normally  parasitic  in  the  small  intestine 
(duodenum)  of  sheep,  camels,  baboons  and  other  animals  and 
occasionally  occurs  in  Egyptian  "  fellahs."  A  closely  allied 
species,  T.  orientalis,  is  found  in  the  duodenum  of  Japanese. 
Other  species  of  this  genus  normally  found  in  herbivorous  ani- 


(ESOPHAGOSTOMUM 


283 


mals  in  Egypt  occasionally  parasitize  man.  The  eggs  of  Tri- 
chostrongylus  (Fig.  61Y)  resemble  those  of  hookworms,  but  they 
are  a  little  larger  and  frequently  contain  more  than  four  cells. 
The  life  history  is  similar  to  that  of  the  hookworms.  Ternidens 
(or  Triodontophorus)  deminutus  (Fig.  106)  is  a  worm  about  half 
an  inch  in  length,  normally  found  in  the  large  intestine  of  monkeys 
in  central  East  Africa,  and  not  uncommon  in  natives;  (Esopha- 
gostomum  apiostomum  (brumpti)  is  a  parasite  which  forms  tumors 
in  the  large  intestine  of  monkeys  and  occasionally  man,  in 
central  Africa  and  in  the  Philippines.     It  produces  symptoms  of 


Fig.  114.  Trichostrongylus  instabilis; 
A,  female,  showing  pointed  tail  and 
vulva  (v.) ;  B,  male,  showing  smaller 
size  and  bursa  (b.).  X  25.  (After 
drawings  and  measurements  by 
Looss.) 


B(XI0) 


Fig.  115.  (Esophagostoma  stepha^ 
nostomum  var.  thomasi.  A,  immature 
female  in  cyst  in  large  intestine  of 
man  in  Brazil;  B,  same,  removed 
from  cyst.     (After  Thomas.) 


dysentery.  An  allied  worm,  0.  stephanostomum  var.  thomasi, 
a  variety  of  a  species  normally  found  parasitic  in  gorillas  in 
Africa,  has  been  found  once  in  man  in  Brazil.  In  this  case  there 
were  187  tumors  (Fig.  115 A)  in  the  small  and  large  intestines 
each  containing  one  worm  (Fig.  115B).  This  species  will  prob- 
ably be  found  to  be  normally  parasitic  in  some  species  of  South 
American  monkey. 

These  and  a  number  of  still  rarer  human  parasites  are  of  little 
interest  as  far  as  man  is  concerned,  except  as  medical  curiosities. 

In  connection  with  the  intestinal  nematodes  there  should  be 
mentioned  three  species  of  spiny-headed  worms  (class  Acantho- 


284 


OTHER  INTESTINAL  ROUNDWORMS 


cephala)  which  occasionally  have  been  found  in  man.  These 
worms  are  not  true  nematodes  but  are  distantly  related  to  them. 
They  are  characterized  by  the  presence,  at  the  anterior  end  of 
the  body,  of  a  prolonged  proboscis  which 
is  covered  with  thornhke,  recurved  spines. 
This  proboscis  is  sunk  into  the  walls  of  the 
intestine  of  the  host  to  gain  anchorage.  Like 
the  tapeworms,  the  spiny-headed  worms  are 
totally  devoid  of  any  digestive  tract  of  their 
own.  The  common  species  of  the  hog, 
Gigantorhynchus  hirudinaceus  (gigas)  (Fig. 
116),  is  said  to  occur  in  man  in  southern 
Russia.  It  is  a  large  worm,  the  female  ten 
to  12  inches  in  length  and  about  one-fourth 
of  an  inch  in  diameter  and  the  male  about 
one-fourth  as  long.  The  larval  stage  is 
passed  in  certain  species  of  beetles. 

A  single  case  of  infection  with  another 
ryhnchus  hirudinaceus  species,  EcMnorhynchus  hominis,  which  was 
'Zasf.''A!rnltur7^ze,  ^nly  one-fourth  of  an  inch  in  length,  has  been 
B,  X  5.  (After  Raiiiet  recorded,  also  from  Russia.  A  species  which 
rom  Neumann.)  -^  probably  more  frequently  a  human  para- 

site is  Moniliformis  (or  EcMnorhynchus)  moniliformis,  normally 
parasitic  in  field  mice,  rats  and  marmots.     The  female  worm  is  a 


Fig.    116.       Giganto- 


o 


Fig.  117.  Development  of  spiny-headed  worm  of  rats  and  mice,  Monilifor- 
mis (or  Echinorhynchus)  moniliformis.  A,  proboscis,  X  50;  B,  larva  from  cock- 
roach,   X  23;    C,  egg,    X  150.     (After  Grassi  and  Calandruccio.) 


little  over  three  inches  in  length,  the  male  about  half  this  size. 
A  species  of  cockroach  serves  as  an  intermediate  host.  Grassi 
and  Calandruccio  found  by  experimentation  that  the  larvae  in 
cockroaches  (Fig.  117B)  would  develop  apparently  equally  well 
in  white  rats  and  in  man.     An  allied  or  possibly  identical  species, 


ACANTHOCEPHALA  285 

M.  clarki,  has  been  described  by  Ward  from  a  squirrel  in  Illinois;  it 
is  a  worm  about  four  or  five  inches  in  length  with  a  very  minute 
proboscis.  Ward  believes  that  this  species  would  also  probably 
develop  in  man  if  the  larvae  were  accidentally  swallowed  with 
some  insect  which  presumably  serves  as  an  intermediate  host. 
A  Moniliformis  which  may  be  identical  with  M.  moniliformis  was 
found  by  the  writer  in  about  ten  per  cent  of  rats  in  Houston, 
Texas,  and  it  has  been  reported  in  other  parts  of  the  United  States 
also. 


CHAPTER  XVI 
TRICHINA  WORMS 

Of  quite  a  different  nature  from  other  intestinal  parasites  is 
the  trichina  worm,  Trichinella  spiralis.  As  far  as  the  injurious- 
ness  of  its  presence  in  the  intestine  is  concerned  it  is  much  less 
serious  than  many  of  the  other  intestinal  worms,  since  its  length 
of  life  as  an  adult  is  relatively  short.  The  serious  and  often 
fatal  results  of  trichina  infection  are  due  to  the  peculiar  life 
history  of  the  worm  and  are  concerned  with  the  offspring  of  the 
infecting  worms  and  not  with  these  worms  themselves. 

There  can  be  little  doubt  but  that  this  worm,  with  the  pork 
tapeworm  as  an  accompKce,  was  responsible  for  the  old  Jewish 
law  against  the  eating  of  pork.  It  was,  however,  many  thousands 
of  years  later,  in  A.D.  1828,  that  the  worms  were  first  dis- 
covered. A  little  over  50  years  later,  1880-1891,  the  trichina 
worm  was  the  cause  of  international  complications  between  the 
United  States  and  Germany,  and  during  this  time  American  pork 
was  excluded  from  German  markets  on  account  of  the  alleged 
frequency  with  which  it  was  found  to  be  infected.  The  outcome 
of  this  trouble  was  the  beginning  of  the  present  American  system 
of  government  meat  inspection. 

Prevalence.  —  Since  the  danger  of  infection  from  eating  im- 
perfectly cooked  pork  has  been  given  wide  publicity,  and  has 
come  about  as  near  to  being  a  matter  of  common  knowledge  as 
any  fact  of  parasitology,  the  prevalence  of  the  infection  has  been 
greatly  reduced,  but  even  now  trichina  embryos  are  found  in 
from  0.5  per  cent  to  2  per  cent  of  the  inhabitants  of  most  civilized 
countries,  as  shown  by  post  mortem  examinations.  According 
to  Dr.  Ransom,  of  the  U.  S.  Bureau  of  Animal  Industry,  statistics 
based  on  microscopic  inspection  of  8,000,000  hogs  in  the  United 
States  show  only  1.41  per  cent  infection  with  live  trichina  worms, 
and  a  total  of  2.57  per  cent  infection  with  live  trichinae  and 
trichina-like  bodies. 

286 


PREVALENCE  287 

In  some  European  countries  the  infection  is  somewhat  less. 
Some  of  the  great  epidemics  of  trichiniasis  (or  trichinosis)  in 
Europe  have  been  attributed  to  American  pork,  but  according 
to  Ransom  there  have  been  no  authentic  cases  of  the  disease  in 
Europe  from  American  pork  up  to  recently,  and,  so  far  as  known, 
none  recently.  Our  slaughterhouses  have  been  referred  to  as  the 
great  breeding  centers  of  trichina,  but  this  is  true  only  as  to 
slaughterhouses  not  under  federal  inspection. 

The  r61e  of  the  rat  in  the  spread  of  trichiniasis  can  readily  be 
appreciated  when  the  statistics  concerning  the  infection  of  these 
animals  in  slaughterhouses,  stables,  etc.,  are  examined.  Of  51 
rats  captured  in  the  Boston  abattoir  some  years  ago  39  (77 
per  cent)  were  infected,  and  every  one  of  40  captured  in  a  large 
exportation  slaughterhouse  in  the  same  city  was  infected.  Rats 
captured  in  stables  where  no  hogs  are  kept,  however,  are  usually 
less  trichinized.  Rats  in  localities  where  an  epidemic  of  tri- 
chiniasis has  recently  swept  through  are  usually  extensively 
infected. 

The  prevalence  of  the  disease  in  man  is  by  no  means  parallel 
with  its  prevalence  in  other  animals.  The  great  controlling 
factor  is  the  method  of  eating  pork.  Among  such  people  as 
Americans,  English  and  French,  where  pork  is  almost  always 
eaten  cooked,  trichiniasis  is  rare  and  comes  only  from  eating 
pork  not  thoroughly  cooked,  thus  allowing  a  few  worms  to  escape, 
though  ordinarily  not  enough  to  cause  serious  disease.  On  the 
other  hand  very  fatal  epidemics  have  occurred  among  the  Ger- 
mans, Austrians  and  Italians,  who  are  very  fond  of  raw  pork, 
especially  in  the  form  of  sausage  or  "  wurst."  Nearly  all  the 
epidemics  in  America  have  been  among  the  Germans  or  Italians 
who  still  cling  to  their  native  habits. 

According  to  statistics  compiled  by  Dr.  Ransom  in  the  five- 
year  period  from  1909  to  1914,  320  cases  occurred  in  the  United 
States,  with  6  per  cent  fatality.  The  majority  of  all  cases  are 
reported  as  being  caused  by  raw  sausage  or  raw  ham,  and  usually 
home-made  or  prepared  in  meat  shops  on  a  small  scale.  As  stated 
by  Ransom,  ''  no  cases  of  trichinosis  have  been  reported  which 
trace  back  to  sausage  prepared  in  establishments  conducted  on 
a  large  scale.  While  it  is  not  impossible  that  such  cases  might 
occur,  the  chances  seem  very  remote,  for  the  reason  that  in  such 
establishments  any  one  lot  of  sausage  is  invariably  made  up  of 


288 


TRICHINA  WORMS 


small  portions  from  a  large  number  of  hogs,  and  the  infection, 
if  any  be  present  among  the  hogs  involved,  is  necessarily  greatly 
diluted,  with  the  result  that  no  individual  consuming  the  sausage 
is  at  all  likely  to  ingest  a  sufficient  number  of  trichinae  to  produce 
an  appreciable  effect,  even  though  the  parasites  should  happen 
to  survive  the  curing  processes  to  which  the  commercially  pre- 
pared sausage  is  usually  subjected." 

Life  History.  —  The  trichina  worm,  Trichinella  spiralis,  occurs 
in  quite  a  large  number  of  animals,  but  the  readiness  with  which 

infection  occurs  in  dif- 
ferent species  of  ani- 
mals varies  greatly. 
In  America  hogs  are 
most  commonly  in- 
fected, and  infection  is 
common  in  rats  which 
have  access  to  waste 
pork;  in  Europe  dogs 
and  cats  commonly 
show  a  higher  percent- 
age of  infection  than 
hogs  in  a  given  local- 
ity. Man  is  highly 
susceptible,  in  fact  so 
susceptible  that  he 
cannot  be  considered 
a  normal  host  of  the 
parasite.  Rats  and 
mice  are  sometimes 
thought  to  be  the  pri- 

FiG.   118.     Larvse  of  trichina  worms,  Trichinella  V>      +  f       +V> 

spiralis,  encysted  in  striped  muscle  fibers  in  pork,  ^l^^ry       noStS       01       tUe 

Camera  lucida  drawing  of  cysts  in  infected  sausage,  worm,  but  the  fact  that 
X  75 

these  rodents  succumb 
easily  to  infection  while  the  parasites  are  still  in  the  intestinal 
stage  tends  to  show  that  rats  are  not  normal  hosts.  Rabbits 
and  guinea-pigs  are  easily  infected  when  fed  meat  containing 
the  worms,  and  a  number  of  other  mammals  can  occasionally 
be  infected  artificially. 

The  worms  gain  entrance  to  the  digestive  tract  as  larvae  en- 
cysted in  meat  (Fig.  118).    In  the  intestine  of  the  host  they  are 


LIFE  HISTORY 


289 


--emb. 


freed  from  their  cysts  and  take  refuge  among  the  villi  and  folds 
of  the  mucous  membrane  of  the  small  intestine.  Here  they 
mature  and  copulate  as  early  as  the  third  day  after  being  swal- 
lowed. The  female  worms  (Fig.  119)  are  from  three  to  four  mm. 
(J  to  J  of  an  inch)  long,  whitish  in  color,  slender  and  tapering 
from  the  middle  of  the  body  toward  the  anterior  end.  The 
digestive  tract  of  the  worm  consists  of  a  long  muscular  pharynx, 
followed  by  a  simple  intestine.  The  forepart  of  the  intestine  has 
a  very  characteristic  cross-barred  ap- 
pearance. The  reproductive  system  in 
both  sexes  is  single,  i.e.,  with  only  one 
ovary  or  testis,  and  occupies  a  large 
portion  of  the  body.  The  arrangement 
is  different  in  the  two  sexes,  the  male 
reproductive  system  opening  at  the 
posterior  end  of  the  body  with  the  anus 
while  the  female  system  opens  on  the 
anterior  third  of  the  body.  The  male 
worms  (Fig.  119)  are  only  about  half 
the  size  of  the  females.  The  adult 
intestinal  worms  are  essentially  short- 
lived, the  males  usually  passing  out  of 
the  intestine  soon  after  mating,  and 
the  females  as  soon  as  they  have  given 
birth  to  all  of  their  offspring.  The 
adults  usually  disappear  within  two  or 
three  months  after  infection. 

^  .  ,  .  V        •      J.U    ^        Fig.     119.     Adult 

iricnina  worms  are  peculiar  m  that  worms,     THchineiia 
they  bring  forth  living  young,  free  of  ^^^^   (^)   ^^^  female  (9); 

,,  ^     ^^  rr^^  ^  ,  •  i      V.,    vulva;    emb.,    embtyos   in 

the  eggshell.  They  do  not  nourish  oviduct;  ov.,  ovary;  t.,  testis, 
their  young  within  the  body  as  do  truly  ^  ^-  ^^^^^r  Claus,  from 
viviparous  animals,  but  merely  retain 

the  eggs  in  the  uterus  until  they  hatch.  Sometimes  the  young 
worms  begin  to  be  born  within  a  week  after  the  parents  have 
been  swallowed  by  the  host.  They  are  most  numerous  in  the 
circulating  blood  between  the  eighth  and  25th  day  after  infection, 
though  the  greatest  invasion  occurs  on  the  ninth  and  tenth  days. 
When  born  they  are  scarcely  0.1  mm.  (^j^^^  of  an  inch)  in  length. 
The  mother  worms  usually  burrow  into  the  walls  of  the  intestine 
far  enough  so  that  the  young  can  be  deposited  directly  into  a 


trichina 

piralis, 


290 


TRICHINA  WORMS 


lymph  or  bloodvessel  rather  than  into  the  lumen  of  the  intestine. 
The  larvae  are  carried  in  the  blood  or  lymph  stream,  and  are 
distributed  to  nearly  all  parts  of  the  body.  They  leave  the 
capillaries  in  the  striped  muscles  and  penetrate  into  the  fibers. 
Although  young  migrating  larvae  may  accidentally  be  carried 
to  other  tissues,  and  have  even  been  found  in  the  cerebrospinal 
fluid  and  in  the  mammary  glands  and  milk  of  a  nursing  woman, 
they  are  apparently  incapable  of  developing  in  any  tissue  except 


Fig.  120.     Larvae  of  trichina  worms  burrowing  in  human  flesh  before  encyst- 
ment.     From  preparation  from  diaphragm  of  victim  of  trichiniasis.      X  75. 

voluntary  muscle.  They  may  settle  in  the  heart  muscle,  but 
degenerate  there  without  continuing  their  development.  The 
muscles  particularly  favored  by  the  worms  are  those  of  the  dia- 
phragm, ribs,  larynx,  tongue  and  eye,  which,  as  noted  by  Staubli, 
are  among  the  most  active  muscles  and  the  muscles  with  the 
richest  blood  supply  and  largest  amount  of  oxygen.  According 
to  Flury  trichinae  have  a  high  glycogen  content,  and  probably 
subsist  on  the  glycogen  stored  in  the  striped  muscles;  in  fact 
the  abundance  of  glycogen  may  account  for  their  location  in 
these  muscles. 


FORMATION  OF  CYSTS 


291 


When  the  larvae  have  arrived  at  their  destination  in  the  muscles 
they  thread  their  way  between  the  fibers  towards  the  ends  of  the 
muscles  (Fig.  120),  ultimately  penetrating  the  individual  fibers 
where  they  coil  up  into  loose  spirals,  constantly  coiling  and  un- 
coiling as  much  as  their  close  quarters  will  permit.  When  worms 
which  are  still  boring  are  teased  out  of  the  flesh  and  warmed  to 
blood  heat,  they  can  be  seen  constantly  tightening  and  loosening 
their  coiled  form,  reminding  one  of  a  fist  being  alternately  clenched 
and  unclenched.  After  entering  muscle  fibers  the  worms  grow 
rapidly  in  size  to  a  length  of  one  mm.  ( jV  of  an  inch),  ten  times  their 
original  size,  and  become  sexually  differentiated.  The  inflam- 
mation caused  by  the  movements  and  waste  products  of  the 
animals  results  in  the  degeneration  of  the  enclosing  muscle  fibers 
and  in  the  formation,  beginning  about  a  month  after  infection, 
of  connective  tissue  cysts  around  the  young  worms.  The  cysts 
(Fig.  118),  which  are  completely  developed  in  from  seven  to  nine 
weeks,  are  lemon-shaped,  from  0.25  to  0.5  mm.  (y^^  to  yV  of  an 
inch)  long,  lying  parallel  with  the  muscle  fibers.  As  a  rule  only 
one  or  two  worms  are  enclosed  in  a  cyst  but  as  many  as  seven  in 
a  cyst  have  been  observed.  When  first  formed  the  cysts  are 
very  delicate  and  can  only 
be  seen  by  careful  focusing 
with  the  microscope,  but 
they  gradually  grow  thicker 
and  more  conspicuous,  and 
after  seven  or  eight  months 
there  begins  a  deposit  of 
chalky    calcareous    matter 

(Fig.   121  A).      This  process  Fio.  121.     Stages  in  calcification  of  trichina , • 

,   .        ,    ,                 1+       '        +V»  '^'  ^^^^  calcified;    B,  thin  layer  of  calcareous 

ultimately     results     in     tne  material  over  whole  cyst,  worm  beginning  to 

entire  cyst  becoming  hard-  degenerate;  C,  complete  calcification.     (After 

J       .    ,                       1  Ostertag.) 

ened     into     a     calcareous 

nodule  (Figs.  121B  and  C),  and  even  the  enclosed  worm, 
which  usually  degenerates  and  dies  after  some  months,  becomes 
calcified  after  a  number  of  years.  There  are  cases,  however, 
where  the  trichina  worms  do  not  die  and  disintegrate  so  soon,  and 
the  calcification  process  is  much  slower.  There  are  records  of 
these  worms  found  living  in  cysts  in  hogs  11  years  after  in- 
fection and  in  man  25  to  31  years  after,  though  it  is  doubt- 
ful whether  in  some  of  these  cases  a  fresh  infection  did  not 


292  TRICHINA  WORMS 

occur  unknown  to  the  patient  or  to  the  observers  who  made 
the  records. 

The  larval  worms,  which,  as  pointed  out  by  Ransom,  on  account 
of  their  advanced  stage  of  development  are  comparable  with 
the  nymphs  rather  than  the  larvae  of  arthropods,  when  encysted 
in  the  flesh  of  some  susceptible  animal  never  develop  further 
until  eaten  by  another  susceptible  animal.  If  they  are  eaten  the 
cyst  is  dissolved  off  in  the  intestine  of  the  new  host,  the  larvae 
are  set  free  in  the  digestive  tract,  and  within  three  days  be- 
come sexually  mature  and  copulate,  to  begin  the  performance 
all  over. 

Obviously  man  usually  if  not  always  becomes  infected  from 
eating  infected  pork,  whereas  hogs  may  be  infected  not  only 
by  eating  scraps  of  raw  pork  but  also  by  eating  the  bodies  of 
infected  rats  and  mice.  The  latter  animals  are  infected  in 
a  similar  manner.  The  number  of  trichina  worms  which  may  be 
harbored  by  a  single  host  is  almost  incredible.  According  to 
the  writer's  investigations,  the  sausage  which  was  the  cause  of  a 
recent  epidemic  in  Portland,  Oregon,  contained  over  2,000,000 
larvae  to  the  pound  at  a  very  conservative  estimate,  and  in  a  bit 
of  human  muscle  from  the  diaphragm  of  an  Italian  who  fell 
victim  to  the  disease  the  number  of  worms  was  even  greater. 

The  Disease.  —  The  disease  caused  by  trichina  worms  is  more 
fatal  to  man  than  to  any  other  animal,  the  fatality  sometimes 
rising  to  30  per  cent  or  more  of  the  cases.  Even  in  man  the 
worms,  if  eaten  only  in  small  numbers,  produce  no  serious  or 
even  noticeable  effect.  When  eaten  in  great  numbers,  however, 
as  would  always  happen  in  eating  heavily-infected  raw  or  under- 
done pork,  the  worms  produce  symptoms  so  much  like  typhoid 
fever  that  the  disease  is  undoubtedly  often  diagnosed  as  such. 
The  course  of  the  disease,  as  described  by  Ransom,  is  somewhat 
as  follows :  the  first  symptoms  of  the  disease  —  diarrhea,  ab- 
dominal pains  and  intestinal  catarrh  —  are  the  result  of  irritation 
of  the  intestine  by  the  adult  worms,  especially  the  females,  which 
burrow  deep  to  deposit  their  young.  Except  in  very  light  cases, 
a  sort  of  general  torpor  is  noticeable,  accompanied  by  weakness, 
muscular  twitching,  etc.  A  very  striking  symptom,  which  ap- 
pears in  about  a  week  and  lasts  for  a  few  days,  is  a  marked  puffi- 
ness  or  edema  of  the  face  and  especially  of  the  eyelids.  As 
pointed  out  by  Ransom,  the  gravity  of  the  case  cannot  be  judged 


SYMPTOMS  293 

from  the  severity  of  the  first  symptoms.     In  some  of  the  worst 
cases  the  first  symptoms  are  very  mild. 

In  nine  or  ten  days  or  longer  the  second  stage  of  the  disease 
appears,  accompanying  the  period  of  migration  of  the  larvse. 
This  is  the  period  which  is  frequently  fatal.  The  most  pro- 
nounced symptoms  are  intense  muscular  pains  and  rheumatic 
aches,  with  disturbances  in  the  particular  muscles  invaded,  in- 
terfering with  the  movements  of  the  eyes,  mastication,  respira- 
tion, etc.,  the  respiratory  troubles  becoming  particularly  severe 
in  the  fourth  and  fifth  weeks  of  the  disease,  in  fact  sometimes 
so  severe  as  to  cause  death  from  dyspnea  or  asthma.  Profuse 
sweating  and  more  or  less  constant  fever,  though  sometimes 
occurring  in  the  first  stage  also,  are  particularly  characteristic 
of  the  second  stage.  The  fever  is  commonly  absent  in  children. 
The  third  stage,  accompanying  the  encystment  of  the  parasites, 
begins  about  six  weeks  after  infection.  The  symptoms  of  the 
second  stage  become  exaggerated,  and  in  addition  the  face  again 
becomes  puffy,  and  the  arms,  legs  and  abdominal  walls  are  also 
swollen.  The  patient  becomes  very  anemic,  skin  eruptions  occur, 
the  muscular  pains  gradually  subside  and  the  swollen  portions 
of  the  skin  often  scale  off.  Pneumonia  is  a  common  compU- 
cation  in  the  third  stage. 

Trichinella  is  unique  among  worms  in  causing  constant  fever. 
It  is  probable  that  the  fever  as  well  as  certain  changes  in  the 
blood  corpuscles  and  chemical  changes  in  the  invaded  muscles 
is  due  both  to  poisonous  substances  given  off  by  the  worms  and 
to  poisonous  substances  resulting  from  destroyed  muscle  tissue. 
Such  substances  have  been  found  by  Flury  and  Groll  and  others 
in  cases  of  Trichinella  infection.  They  are  substances  which 
act  on  the  muscles  themselves,  on  the  nervous  system,  and  on  the 
bloodvessels.  It  is  quite  evident,  as  pointed  out  by  Herrick,  that 
with  the  invasion  of  the  blood  and  tissues  by  millions  of  larvae 
and  with  the  breaking  down  of  large  amounts  of  muscle  tissue 
a  constant  inoculation  of  the  infected  person  with  poisonous 
protein  material  is  taking  place,  a  condition  which  always  gives 
rise  to  fever.  Certain  volatile  acids  are  produced  by  the  muscle 
degeneration,  and  these  are  considered  by  Flury  to  account  for 
the  muscular  pains.  Other  toxic  substances  account  for  most  of 
the  other  symptoms  of  the  disease,  e.g.,  the  marked  increase  in 
certain  kinds  of  white  blood  corpuscles,  the  eosinophiles. 


294  TRICHINA  WORMS 

The  duration  and  final  outcome  of  the  disease  is  variable, 
according  to  the  heaviness  of  the  infection.  Death,  as  remarked 
before,  may  frequently  result,  and  according  to  Ransom  most 
commonly  occurs  from  the  fourth  to  the  sixth  week.  It  rarely 
occurs  before  the  end  of  the  second  week  or  after  the  seventh. 
Recovery  usually  does  not  occur  in  less  than  from  five  to  six 
weeks  after  infection,  and  often  not  for  several  months.  Re- 
current muscular  pains  and  weakness  may  continue  for  years  and 
a  stiffness  may  persist  indefinitely  in  the  invaded  muscles.  Com- 
monly cases  in  which  a  copious  diarrhea  appears  early  in  the 
disease  are  of  short  duration  and  mild  in  type.  Young  children, 
due  either  to  smaller  quantities  of  pork  eaten  or  to  greater  tend- 
ency to  diarrhea,  are  likely  to  recover  quickly. 

Treatment  and  Prevention.  —  The  search  for  a  specific  remedy 
for  trichiniasis  has  so  far  been  futile.  Even  the  adult  worms  in 
the  intestine  are  much  more  difficult  to  dislodge  or  destroy  than 
are  other  intestinal  worms,  since  they  bore  so  deeply  into  the 
intestinal  walls  that  the  ordinary  drugs  do  not  affect  them.  Even 
were  it  possible  to  drive  out  the  adults  readily,  this  often  could  not 
be  done  in  time  to  prevent  disease  or  death,  since  the  infection  is 
seldom  recognized  before  the  larvae  are  already  produced  and  are 
migrating  throughout  the  body.  This  is  the  critical  stage  of  the 
disease;  if  the  system  can  endure  the  irritation  and  inflam- 
mation produced  by  the  burrowing  of  millions  of  worms  and 
can  withstand  the  effects  of  the  toxins  produced  both  from  the 
worms  themselves  and  from  the  destroyed  tissues  during  the 
first  and  heaviest  onslaught  of  the  newly  produced  larvae,  the 
danger  is  past.  The  fever,  the  muscular  pains,  amounting  to 
agony  for  a  time,  and  the  intestinal  disorders  continue  for  weeks 
but  gradually  subside.  The  treatment  employed  during  all  this 
time  can  only  be  systematic  and  of  general  nature  —  efforts  to 
reduce  the  fever,  to  permit  sleep,  to  keep  the  digestive  system 
in  as  good  order  as  possible  and  to  do  all  that  can  be  done  to  keep 
up  the  vitality  and  general  health. 

It  is  possible  that  if  the  trichina  worms  could  be  isolated  and 
ground  up,  and  injected  into  the  blood,  an  active  immunity 
could  be  built  up  as  in  the  case  of  typhoid  vaccinations.  Passive 
immunity  by  injection  of  serum  from  a  convalescent  has  been 
stated  by  Salzman  to  have  some  curative  as  well  as  preventive 
value,  but  this  work  needs  confirmation.     The  disease,  however, 


PREVENTION  295 

is  not  so  prevalent  or  so  difficult  to  prevent  by  otfier  means  as 
to  make  promiscuous  immunization  justifiable,  even  if  possible. 
A  more  hopeful  though  so  far  unproductive  line  of  research 
regarding  the  treatment  of  the  infection  lies  in  experiments 
with  drugs  or  serum  to  kill  either  the  adult  worms  in  the  intestine 
or  the  larvae  before  they  begin  destroying  the  tissues. 

Personal  preventive  measures  against  trichiniasis  are  easy 
and  consist  simply  in  abstinence  from  all  pork  which  is  not 
thoroughly  cooked.  Experiments  by  the  U.  S.  Bureau  of  Animal 
Industry  show  that  trichinae  are  quickly  destroyed  by  a  tem- 
perature of  55°  C.  (131°  F.),  since  the  body  protoplasm  is  coagulated 
at  this  temperature,  but  pork  must  be  cooked  for  a  length  of  time 
proportionate  to  its  weight  in  order  to  insure  the  permeation 
of  heat  to  the  center.  Experiments  show  that  at  least  30  to 
36  minutes  boiling  should  be  allowed  to  each  kilogram  of  meat 
(2^  lbs.).  Hurried  roasting  does  not  destroy  the  parasites  as 
long  as  red  or  raw  portions  are  left  in  the  center.  Cold  storage 
for  20  days  or  more  at  temperatures  below  10°  F.  has  been  shown 
by  Ransom  to  be  destructive  to  trichinae.  The  regulations  of 
the  U.  S.  Bureau  of  Animal  Industry,  relative  to  pork  prod- 
ucts customarily  to  be  eaten  without  cooking,  require  freez- 
ing for  20  days  at  a  temperature  of  not  higher  than  5°  F., 
or  curing  in  accordance  with  certain  specified  processes. 
Temperatures  above  10°  F.  are  more  or  less  uncertain  in 
their  effects.  Salting  and  smoking  are  not  efficacious  unless 
carried  out  under  certain  conditions.  Thorough  salting  is  effec- 
tive, provided  the  meat  is  left  for  some  time  for  the  salt  to  per- 
meate it.  Large  pieces  of  pork  placed  in  brine  have  been  known 
to  contain  living  trichinae  for  over  a  month.  The  parasites  in 
sausages  are  destroyed  in  24  hours  by  hot  smoking  whereas  they 
resist  cold  smoking  for  three  days. 

Prevention  of  trichiniasis  by  meat  inspection  methods  is  at  best 
only  partial,  and,  while  meat  inspection  might  help  to  lessen  the 
chances  of  the  disease,  it  should  not  be  implicitly  relied  upon. 
Probably  in  an  ordinary  meat  inspection  all  heavy  infections 
would  be  found,  provided  the  inspector  has  been  doing  his  work 
properly.  The  inspection  usually  consists  in  the  microscopic  ex- 
amination of  a  bit  of  muscle  from  tongue  and  diaphragm;  if 
the  examination  is  negative,  the  hog  is  passed.  Obviously  light 
infections  must  frequently  escape  notice,  and  the  false  sense  of 
security  which  is  the  result  of  knowledge  that  meat  has  been 


296  TRICHINA  WORMS 

''  inspected  "  may  do  much  damage.  There  is  no  inspection 
for  trichinae  in  force  in  the  United  States  at  the  present  time. 

Much  could  be  done  to  prevent  the  prevalence  of  trichina  in- 
fection in  pork  by  preventing  hogs  from  eating  food  which  might 
be  infected.  Hogs  should  never  be  allowed  access  to  the  car- 
casses of  other  hogs  or  to  the  dead  bodies  of  rats  and  mice,  or 
to  waste  scraps  of  pork.  Dead  hogs  or  waste  pork,  if  there  is 
any  possibility  of  their  being  infected,  should  not  be  thrown  where 
rats  and  mice  could  prey  upon  them.  If  these  principles  were 
carefully  followed  out,  there  is  no  doubt  but  that  trichiniasis 
could  be  reduced  to  a  much  greater  extent  than  it  has  been. 

The  symptoms  of  trichina  disease  in  hogs  are  much  less  evident 
than  in  man,  and  there  is  no  certain  diagnosis  of  it  in  living  ani- 
mals except  by  microscopic  examination  of  the  muscles  for  the 
detection  of  the  larvae.  When  heavily  infected,  hogs  show  severe 
intestinal  disorders,  abdominal  pains  and  stiff  muscles,  but  there 
is  nothing  diagnostic  in  these  symptoms.  A  farmer  who  drives 
sick  hogs  to  market,  however,  in  order  to  get  rid  of  them,  with- 
out giving  proper  warning  of  their  condition  which  might  make 
possible  the  discovery  of  trichina  infection  if  present,  should 
be  considered  guilty  of  criminal  negligence,  and  punished  in 
accordance  with  the  damage  done  by  this  neghgence.  This  is 
particularly  true  if  he  feeds  his  hogs  waste  containing  raw  meat, 
or  allows  them  to  feed  upon  dead  animals  —  a  very  common 
practice. 

As  has  recently  been  pointed  out  by  Stiles,  there  is  no  prac- 
tical or  proper  method  of  inspecting  meat  by  which  the  absence  of 
Trichinella  can  be  guaranteed,  and  it  is  therefore  unjust  to  hold 
a  butcher  responsible  for  cases  of  trichiniasis  which  may  result 
from  the  eating  of  pork  sold  by  him.  There  are  laws  which  pro- 
vide that  ^'  diseased  meat  "  shall  not  be  sold  and  that  an  implied 
warranty  of  fitness  for  food  goes  with  any  sale  of  food.  Neither 
of  these  laws,  however,  can  be  unreasonably  enforced.  Techni- 
cally all  meat  is  diseased,  since  there  are  no  market  animals 
which  are  not  parasitized  in  some  way.  As  to  the  "  implied 
warranty,"  this  can  go  only  with  an  implied  guarantee  on  the 
part  of  the  buyer  that  the  food  will  be  properly  prepared  before 
being  eaten.  Clams  in  the  shell,  unhusked  corn  and  uncooked 
beans  are  guaranteed  as  being  fit  for  food  only  when  properly 
prepared.     In  like  manner  pork  is  sold  with  the  understanding 


FITNESS  OF  PORK  FOR  FOOD  297 

that  it  will  be  properly  prepared,  i.e.,  thoroughly  cooked.  Raw 
pork,  since  it  is  likely  to  contain  Trichinelloe  which  may  cause 
disease,  and  since  the  absence  of  these  worms  cannot  be  guaran- 
teed by  any  practical  inspection  now  known,  is  unfit  for  food  and 
therefore  cannot  be  guaranteed  if  eaten  raw.  As  Stiles  has 
pointed  out,  great  and  unjustifiable  loss  may  result  from  too 
stringent  enforcement  of  the  laws  mentioned  above. 


CHAPTER  XVII 
PILARIS   AND   THEIR  ALLIES 

General  Account.  —  One  of  the  most  interesting  and  puzzling 
groups  of  human  parasites  are  the  members  of  the  nematode 
genus  Filaria.  They  are  extremely  common  parasites  in  all 
tropical  countries,  have  a  unique  and  extraordinary  life  history, 
are  associated  with  many  serious  pathological  conditions  and 
have  figured  prominently  in  the  history  of  medical  science. 

Dr.  Timothy  R.  Lewis  first  discovered  these  worms  swarming  in 
human  blood,  while  working  on  tropical  diseases  in  India.  They 
had  previously  been  observed  in  various  bodily  excretions  but 
only  in  rare  cases  and  in  small  numbers.  They  were  found 
in  enormous  numbers  in  the  blood,  but  only  at  night.  The 
worms  were  evidently  larvae  and  since  they  only  rarely  and  ap- 
parently accidentally  escaped  from  the  body  with  excretions, 
the  thought  occurred  to  Manson  that  they  must  be  liberated 
from  the  blood  by  some  nocturnal  blood-sucking  insect.  Man- 
son  and  others  later  proved  this  theory  to  be  correct,  and  thus 
took  the  first  step  toward  our  present  knowledge  of  the  biologi- 
cal transmission  of  disease  by  insects,  a  step  which  marked  the 
beginning  of  a  new  era  in  modern  medicine. 

Many  species  of  Filaria  from  human  blood  have  been  described, 
some  of  which  undoubtedly  are  not  valid  species.  Some  species 
apparently  produce  no  pathological  conditions  whatever,  while 
others  are  associated  with,  and  are  usually  considered  to  be  the 
direct  cause  of,  a  large  number  of  diseased  conditions.  Some  of 
the  species  are  of  limited  geographic  distribution  while  others 
are  of  world-wide  range,  probably  due  to  differences  in  the  ex- 
tent of  the  distribution  of  the  intermediate  host.  In  some 
tropical  localities  50  per  cent  or  more  of  the  population  are  para- 
sitized by  these  animals.  In  South  China  ten  per  cent  of  the  entire 
population  is  said  to  be  infected  and  in  some  South  Sea  Islands 
over  half  of  the  inhabitants  are  infected.  Recently  in  an  exam- 
ination of  949   natives  from  the   Congo-Cameroon   country  of 

298 


LIFE  HISTORY  OF   FILARIA   BANCROFTI  299 

Africa,  about  74  per  cent  of  the  men,  79  per  cent  of  the  women  and 
33  per  cent  of  the  children  were  found  to  be  filariated. 

The  blood-dweUing  filarise  which  are  readily  observed  are,  as 
remarked  above,  only  larvae,  the  adults  being  much  larger,  long, 
slender  worms  which  live  in  the  lymphatic  vessels,  connective 
tissue  or  other  tissues  of  the  body.  It  is  to  these  adult  worms 
and  not  to  the  larvae  that  the  so-called  "  filarial  diseases  "  are 
supposed  to  be  due;  the  blood-living  worms  apparently  cause 
no  serious  symptoms.  The  larvae  have  been  termed  "  micro- 
filariae "  to  distinguish  them  from  the  adult  worms. 

Filaria  hancrofti 

The  most  widespread  species  and  most  important  from  a 
medical  point  of  view  is  Filaria  hancrofti.  This  nematode  occurs 
more  or  less  abundantly  in  all  warm  climates  of  the  world,  north 
to  southern  United  States  and  southern 
Europe  and  Asia,  and  south  to  southern 
Australia  and  Patagonia. 

Life    History.  —  The    adult    Filarice 
were    not    discovered    for    many    years      pio.  122.   Adults  of  Filaria 
after  the  larvae  had  been  found  in  the  hancrofti,    female   ( 9 )    and 

1  1        T         .  ,,  •       j.1.        J  male     ($).       Natural     size. 

blood,    smce    they   occur  in   the   deep-  ^^f^^j.  Manson.) 
seated  lymphatic  vessels  where  they  could 

be  observed  only  on  post  mortem  examinations.  They  are  very 
long,  slender  nematodes  (Fig.  122),  the  females  three  or  four  inches 
in  length  and  hardly  greater  in  diameter  than  a  horsehair,  and 

the  males  about  half  this  size.     In  their 
normal  habitat  in  the  lymph  vessels  the 
males  and   females  live    coiled   up   to- 
gether, sometimes  several  pairs  of  them 
Fig.  123.    Microfilaria  of  in  a  knot.     The  male  worms,  in  addition 
~uteTu:t  pai'e^rr  to   their   smaller   size,   may   be   distin- 
rounded  by  delicate  mem-  guishcd  from  the  females  by  the  coiled 
brane.    (After  Bahr.)  ^^.^  ^j^.^^  reminds  One  of  a  vine  tendril. 

The  greater  part  of  the  body  of  the  female  is  occupied  by  a  pair 
of  uteri,  which  in  the  adult  are  always  filled  with  eggs. 

The  eggs  (Fig.  123)  usually  hatch  before  they  are  laid  so  that 
living  young  swarm  forth  from  the  parent  worm,  but  in  excep- 
tional cases  the  eggs  are  deposited  before  hatching.     The  young 


c^   %^ 


300 


FILARliE  AND  THEIR  ALLIES 


worms  reach  the  blood  by  way  of  the  lymph  stream  and  these 
grow  to  about  300  /x  (a  little  over  j^^  of  an  inch)  in  length.  They 
are  delicate  colorless  worms  (Fig.  124A),  blunt  at  the  anterior 
end  and  tapering  to  a  slender  point  at  the  tail  end,  and  are 
entirely  enclosed  in  a  remarkably  delicate  transparent  sheath, 
which,  although  it  fits  as  tightly  as  a  glove  over  a  finger,  is  too 
long  for  the  animal  and  can  be  seen  projecting  at  either  end.  The 
sheath  may  be  looked  upon  as  a  wonderful  adaptation  to  prevent 

the  worms  from  being  able  to 
bore  through  the  bloodvessels 
and  escape  from  the  blood,  in 
which  case  they  would  miss 
their  chance  for  "  salvation." 
The  internal  organs  are  in  a 
very  rudimentary  condition. 
The  most  remarkable  cir- 
cumstance connected  with  the 
life  of  these  microfilariae  is  the 
periodical  appearance  and  dis- 
appearance of  them  in  the 
blood  of  the  peripheral  vessels. 
If  the  blood  of  an  infected 
person  is  examined  during  the 
day  few  if  any  worms  can  be 
found,  but  as  evening  ap- 
proaches they  begin  to  appear 
Fig.  124.    Comparison  of  microfiiariffi ;  and  Continue  to  increase  Until 

A  mf.  bancrofti  (large  with  «heath) ;  5,  ^^^^  midnight,  after  which 
mf.  Persians  (small,  blunt  tail,  no  sheath);  ^      ' 

c,  mf.  loa  (large,  with  sheath);  D,  mf.  they     decrease     again     until 

juncea  (demarquaii)   (small,  sharp  tail,  no    rnnrm'ncr        "Hnrino-    +V>p    niaVit 

sheath).     X75.    (After  Manson.)  mornmg.     uurmg  tne   nignt 

when  they  are  most  abun- 
dant there  may  be  as  many  as  500  worms  in  a  single  drop  of 
blood.  If  the  parasites  are  assumed  to  be  evenly  distributed 
throughout  the  peripheral  circulation,  this  would  imply  the 
presence  of  several  milHon  worms  in  the  body.  The  periodic 
appearance  and  disappearance  of  microfilariae  in  the  blood  is  not 
invariable.  When  an  infected  person  is  made  to  sleep  in  the 
daytime  instead  of  at  night,  the  appearance  and  disappearance 
of  the  parasites  in  the  peripheral  bloodvessels  can  be  reversed, 
implying  that  the  distribution  of  the  parasites  may  be  dependent 


FILARIA  BANCROFTI  IN   MOSQUITOES  301 

on  some  physiologic  condition  of  the  host.  Still  stranger  is  the 
fact  that  in  many  of  the  South  Sea  Islands,  Samoa,  the  Fiji 
Islands  and  the  Philippine  Islands,  the  microfilariae  show  no 
periodic  disappearance,  although  if  a  person  infected  in  a  place 
where  the  parasites  do  show  periodicity  be  transferred  to  one  of 
the  above-named  islands,  the  periodic  phenomena  still  persist. 
As  stated  before,  Manson,  the  great  English  parasitologist,  with 
characteristic  ingenuity,  suspected  that  this  parasite,  so  abundant 
in  the  blood,  must  make  use  of  some  blood-sucking  insect  as  a 
means  of  transmission,  and  further  concluded  that  the  night 
swarming  of  the  parasites  in  the  peripheral  circulation  might  be 
an  adaptation  to  the  nocturnal  habits  of  an  intermediate  host. 
Working  on  this  hypothesis,  he  discovered  that  certain  mosquitoes 
acted  as  the  liberating  agents  for  the  parasites.  The  fact  that 
in  those  islands  where  no  periodicity  is  shown  the  usual  inter- 
mediate host  is  a  diurnal  mosquito  Aedes  (or  Stegomyia)  pseudo- 
cutellaris,  certainly  bears  out  the  adaptation  hypothesis.  On  the 
grounds  of  the  apparently  distinct  habits  and  different  adaptation, 
the  non-periodic  microfilariae  have  been  separated  into  a  distinct 
species,  or  at  least  subspecies,  to  which  the  name  Filaria  philip- 
pinensis  was  applied  by  Ashburn  and  Craig  in  1906.  Zoologists 
are  coming  more  and  more  to  realize  the  importance  of  physio- 
lologic  as  well  as  morphologic  characteristics  as  a  basis  for  sepa- 
rating species  and  subspecies.  The  case  of  these  filariae  is  by  no 
means  unique  in  the  organic  world.  Physiologic  and  biochemical 
reactions  are  the  main  basis  for  the  classification  of  the  Bacteria, 
and  some  Protozoa  can  be  distinguished  better  by  their  patho- 
genic effects  and  biochemical  reactions  than  by  their  morphology. 
To  continue  their  development  the  larval  worms  must  be 
sucked  up  by  the  females  of  certain  species  of  mosquitoes.  A 
considerable  number  of  species  of  mosquitoes  of  several  different 
genera,  including  Anopheles,  Aedes  and  Culex,  may  serve  as 
intermediate  hosts  for  F.  bancrofti  (see  p.  449).  The  commonest 
and  most  widespread  transmitting  agent  is  the  house  mosquito 
of  the  tropics,  Culex  quinquefasciatus  (fatigans),  a  species  which 
also  transmits  dengue.  A  few  hours  after  being  swallowed  by 
a  susceptible  mosquito  the  microfilariae  (Fig.  125 A)  become  rest- 
less and  endeavor  to  escape  from  their  sheaths.  This  they 
eventually  accompUsh  by  butting  against  the  anterior  end, 
having  gained  as  much  impetus  as  their  close  quarters  will  allow. 


302 


PILARIS  AND  THEIR  ALLIES 


Once  free,  the  little  larvae  (Fig.  125B)  move  actively  about  in 
quite  a  different  manner  from  the  ineffective  wriggling  in  which 
they  indulged  while  enclosed  in  the  sheath,  and  by  means  of  which 
they  were  unable  to   "  get  anywhere."     The  active  liberated 

worms  make  their  way 
to  the  thoracic  muscles 
of  the  mosquito,  where 
they  He  between  the 
muscle  fibers  and  par- 
allel with  them.  The 
body,  growing  rapidly, 
by  the  fourth  to  tenth 
day  becomes  thick  and 
sausage-like  (Fig. 
125C),  with  a  short, 
pointed  tail,  but  it  later 

Fig.  125.      Development  of  Filaria  bancrofti  in  increases    greatly    in 

mosquito;  A,aswithdrawnwithblood(first24hours^  j^^^j^  ^^^  decreases 
in  stomach;   B,  form  found  m  tissues  just  outside  ^ 

stomach  (48  to  72  hours  after  ingestion) ;  C,  form  slightly     in      thickueSS, 

found  in  muscles  on  fourth  day;  i)  mature  larval  thuS  becoming  long  and 
lorm,  ready  for  transmission,  in  proboscis  (two  or  .  . 

more  weeks  after  ingestion).     X  150.     (After  Lewis  slender     again     (Fig. 

from  Nuttaii.)  125D).    Meanwhile  the 

internal  organization  of  the  animal  undergoes  a  great  change. 
The  central  core  of  cells  gradually  becomes  differentiated  into  a 
digestive  tract,  separated  from  the  body  wall  by  a  true  body 


Fig.  126.     Mature  larvae  of  Filaria  bancrofti  in  thoracic  muscles  and  prob 
of  mosquito.     (After  Castellani  and  Chalmers.) 


cavity.  By  the  time  the  larva  has  reached  its  full  size  —  about 
1.5  mm.  {^^  of  an  inch)  in  length  —  the  digestive  tract  is  a  com- 
plete tube  with  both  mouth  and  anal  openings.  While  these 
changes  are  taking  place,  the  larval  worm,  though  capable  of 
activity,  remains  at  rest  between  the  muscle  fibers  (Fig.  126), 


FILARIAL  DISEASES  303 

but  it  now  becomes  active  again  and  migrates  into  the  connective 
tissue  of  the  anterior  parts  of  the  body  of  its  host,  and  ultimately 
into  the  proboscis  (Fig.  126).  Here  the  worms  lie  in  pairs,  or 
several  pairs  together,  awaiting  an  opportunity  to  re-enter  a 
human  host. 

The  length  of  time  required  for  the  metamorphosis  and  de- 
velopment in  the  mosquito  varies  from  about  two  weeks  under 
ideal  conditions  to  several  weeks  under  less  favorable  circum- 
stances. When  the  infected  mosquito  bites  a  human  being,  the 
worms  emerge  from  the  proboscis  and  bore  through  the  skin 
in  the  immediate  vicinity  of  the  wound,  though  not  directly 
through  the  puncture.  Experiments  have  shown  that  the  larvae 
can  not  be  deceived  into  entering  vegetable  tissue,  such  as  a 
banana,  even  though  for  many  days  they  have  been  at  the  tip 
of  the  proboscis,  ready  to  emerge  when  the  mosquito  bites  into 
warm-blooded  flesh. 

It  is  possible  that  these  parasites  may  occasionally  find  entrance 
to  the  human  body  by  other  paths  than  the  mosquito's  bite  but 
this  has  not  yet  been  proved.  The  popular  belief  that  bad  water 
is  the  cause  of  filarial  infection  is  probably  due  to  the  effect  of 
stagnant  water  on  the  abundance  of  mosquitoes,  and  not  to  the 
emergence  of  the  larvae  from  the  bodies  of  mosquitoes  into  water. 
Bahr  has  shown  that  the  larvae  will  live  in  water  only  seven 
hours. 

Once  back  in  a  human  body  from  this  period  of  "  purgatory  " 
in  the  body  of  a  mosquito  the  larvae  migrate  to  the  lymphatic 
vessels,  there  to  attain  sexual  maturity,  copulate  and  reproduce. 
The  larvae  of  the  next  generation  escape  again  to  the  blood  as 
microfilariae,  and  the  cycle  is  complete.  The  adult  worms  may 
five  for  many  years  and  even  the  microfilariae  are  able  to  live  for 
a  considerable  time,  as  shown  by  their  continued  presence  after 
the  death  of  the  parents. 

Filarial  Diseases.  —  The  disease  symptoms  which  are  asso- 
ciated with  Filaria  hancrofti  can  all  be  traced  to  interference 
with  the  lymphatic  system.  In  many  cases  there  are  no  ill 
effects  of  the  infection  felt  for  many  years,  or  perhaps  never, 
though  sooner  or  later  there  is  usually  produced  anemia,  en- 
largement of  the  spleen  and  fever.  More  serious  are  the  effects 
produced  by  obstruction  of  the  lymphatics.  This  causes  great 
enlargement  of  the  lymph  vessels  and  the  diversion  of  the  lymph 


304 


FILARI^  AND  THEIR  ALLIES 


from  its  normal  channel,  and  results  in  varicose  lymph  glands 
(Fig.  127C)  and  vessels  and  in  distended  lymph  sacs  which  may 
burst  into  the  kidneys,  bladder  or  body  cavity.  Often  the 
microfilariae  disappear  from  the  blood,  probably  on  account  of  the 
death  of  the  parents,  but  the  obstruction  of  the  lymphatics 
continues  to  exist,  as  do  the  evil  effects  resulting  therefrom. 


Fig.  127.  A  few  extreme  cases  of  elephantiasis;  A,  of  legs  and  feet;  B,  of 
scrotum;  C,  varicose  groin  gland;  Z),  of  scrotum  and  legs;  E,  of  mammary  glands. 
{A  and  B  sketched  from  photos  from  Castellani  and  Chalmers;  C,  D  and  E  from 
Manson.) 

One  of  the  most  frequent  results  of  a  blocking  of  the  lymph 
vessels  is  an  enormous  enlargement  of  the  part  of  the  body 
in  which  the  blocking  occurs,  known  by  the  suggestive  name, 
"■  elephantiasis  "  (Fig.  127).  In  most  cases  the  lower  Hmbs  and 
scrotum  are  the  parts  affected,  though  almost  any  portion  of 


FILARIAL  DISEASES  305 

the  body  may  occasionally  become  enlarged.  In  some  South 
Sea  Islands  50  per  cent  or  more  of  the  population  are  thus  affected. 
The  disease  begins  by  repeated  attacks,  at  intervals  of  from  a 
month  to  a  year,  of  ''  elephantoid  "  or  filarial  fever  in  which 
chills  and  high  fever  accompany  a  painful  swelling  of  the  parts 
affected.  These  attacks,  also  known  as  lymphangitis,  end  in  an 
emission  of  lymph  and  a  partial  subsidence  of  the  swelling. 
But  each  attack  leaves  a  little  more  permanent  tissue,  so  that  in 
time  the  growth,  which  is  hard  and  unyielding,  develops  to  enor- 
mous proportions.  Sometimes  an  affected  leg  may  reach  a  diam- 
eter of  several  feet.  In  one  case  recorded  by  Manson,  a  scrotum 
affected  by  elephantiasis  reached  a  weight  of  224  pounds,  though 
it  must  be  admitted  that  this  is  unusual. 

Another  condition  resulting  from  filarial  infection  is  the  escape 
of  the  contents  of  lymph  vessels  into  the  kidneys  or  bladder,  a 
condition  technically  known  as  "  chyluria."  The  urine  is  milky 
and  coagulates  after  standing  a  short  time.  This  condition  lasts 
for  a  few  days  or  weeks,  then  ceases  and  returns  at  irregular 
intervals.  It  produces  severe  anemia  and  a  general  feeling  of 
ennui,  and  saps  the  vitality. 

Occasionally  the  presence  of  dead  filarise  in  the  body  leads  to 
the  formation  of  abscesses  which  sooner  or  later  discharge.  If 
on  any  of  the  appendages,  no  further  trouble  results,  but  such 
abscesses  in  the  internal  regions  of  the  body  may  have  serious  or 
fatal  effects. 

Though  very  probably  some  of  these  so-called  "  filarial  dis- 
eases "  are  caused  directly  by  the  filarise,  the  exact  relation  of 
F.  bancrofti  to  all  of  the  pathological  conditions  associated  with 
its  presence  in  the  body  is  far  from  settled.  Dutcher  and  Whit- 
marsh,  of  the  United  States  Army,  in  investigations  of  filarial 
diseases  in  Porto  Rico  recently  obtained  pure  cultures  of  a  certain 
type  of  bacterium  from  the  blood  or  serum  of  15  patients,  all 
but  one  of  whom  was  affected  by  some  form  of  filarial  disease, 
whereas  in  unaffected  individuals,  with  one  exception  which  was 
looked  upon  as  a  "  carrier,"  the  cultures  from  the  blood  remained 
uniformly  sterile.  In  a  few  cases  in  which  filarial  diseases  were 
present  the  bacterium  was  not  found  but  it  was  believed  that 
either  the  infection  was  so  light  that  the  cultures  did  not  happen 
to  become  contaminated,  or  that  the  infection  had  died  out. 
A  number  of  other  observers  have  obtained  cultures  of  bacteria 


306  FILARI.E  AND  THEIR  ALLIES 

from  blood  and  tissues  of  elephantiasis  cases.  Others,  however, 
have  found  the  blood  quite  sterile.  It  is  worth  noting  in  this 
connection  that  the  number  of  cases  of  elephantiasis  or  other 
filarial  diseases  in  which  microfilariae  are  not  present  in  the  blood 
is  considerably  greater  than  those  in  which  the  larval  parasites 
are  present.  This  is  usually  explained  by  assuming  that  the 
parent  filarise  have  died  or  that  the  larvae  cannot  reach  the  blood 
on  account  of  a  blocking  of  the  lymph  channels  by  fibrous  growths. 
Cruickshank  and  Wright,  for  instance,  in  130  cases  of  elephantiasis 
in  Cochin,  found  only  12  with  microfilariae  in  the  blood.  The 
observations  recorded  above  are  certainly  significant  and  may 
revolutionize  our  ideas  in  regard  to  filarial  diseases.  However, 
even  if  some  of  the  "  filarial  diseases  "  were  found  to  be  due  to 
bacteria,  the  filariae  might  still  be  incriminated  as  carriers  of 
the  bacteria,  and  therefore  as  an  indirect  cause  of  the  diseases. 
Treatment  and  Prevention.  —  So  far  there  is  no  widely-ac- 
cepted treatment  by  which  the  parent  filariae,  and  with  them  the 
microfilariae,  can  be  destroyed.  The  number  of  the  larvae  is 
reduced,  however,  by  injections  of  thymol,  ichthyol  and  other 
drugs,  and  such  injections  might  prove  to  be  a  useful  preventive 
measure.  McNaughton  has  recently  reported  five  cases  of 
filarial  infection  successfully  treated  by  injections  of  salvarsan; 
one  case  was  of  ten  years'  standing.  Usually  the  only  course 
of  the  physician  is  to  relieve  as  far  as  possible  the  abnormal 
conditions  associated  with  the  presence  of  the  worms.  Such 
relief,  of  course,  varies  greatly  with  the  diverse  pathological 
conditions  which  may  arise.  Varicose  glands  and  vessels,  un- 
less causing  great  discomfort,  are  usually  left  alone,  since  they 
are  lymph  channels  substituted  for  the  normal  ones  in  the  body 
which  have  been  blocked,  and  it  is  therefore  dangerous  to  inter- 
fere with  them.  In  cases  of  elephantoid  fever  the  only  treat- 
ment is  such  as  would  tend  to  relieve  the  pain  in  the  swellings 
and  the  fever,  and  perhaps  in  severe  cases  the  pricking  of  the 
swollen  part  to  allow  the  exudation  of  the  collecting  lymph. 
In  chyluria  the  treatment  consists  in  rest  and  in  making  the 
pelvic  regions  as  comfortable  as  possible  to  prevent  pressure 
which  would  tend  to  burst  the  lymphatics  and  force  the  lymph 
into  the  kidneys  or  bladder.  Elephantiasis,  the  commonest 
expression  of  filarial  disease,  is  seldom  completely  recovered 
from.     Formerly  the  only  treatment  was  temporary  reduction 


FILARIA  PERSTANS  307 

of  the  swellings  and  prevention  of  further  growth  by  care  of  the 
general  health,  avoidance  of  violent  exercise,  massage  and  tight 
bandaging.  In  severe  cases  of  elephantiasis  of  the  leg  physicians 
sometimes  cut  off  great  masses  of  the  elephantoid  tissue,  grafting 
on  new  pieces  of  skin  to  cover  the  parts  operated  on.  Removal 
of  enlarged  growths  of  the  scrotum  can  usually  be  accomplished 
successfully.  Another  method  which  has  been  used  with  some 
success  is  an  operation  for  the  draining  of  the  lymph  from  the 
tissue  all  the  way  into  the  bone  or  even  from  the  bone  itself. 

Castellani  has  recently  found  a  method  of  reducing  elephantoid 
tissue  which  will  probably  supplant  all  of  the  above  methods. 
This  consists  in  the  injection  into  the  diseased  tissues  of  a  drug, 
fibrolysin,  which,  as  its  name  implies,  has  the  property  of  destroy- 
ing fibrous  connective  tissue.  Elephantoid  swellings  are  re- 
ported to  have  been  cured  by  this  method  in  a  few  months. 

Prevention  of  filarial  diseases  can  best  be  accomplished  by 
anti-mosquito  campaigns.  As  far  as  is  known  at  present  mos- 
quitoes are  the  only  means  of  transmission  which  the  parasites 
have.  The  same  preventive  measures,  therefore,  which  serve 
as  preventives  against  malaria,  serve  also  against  Filaria  han- 
crofti,  and  since  the  former  disease  is  found  practically  every- 
where that  the  filarise  are  found,  it  is  possible  to  prevent  the 
two  diseases  with  one  effort.  People  who  carry  filariae  in  their 
blood  should  be  prevented,  as  far  as  possible,  from  exposing 
themselves  to  mosquitoes.  In  the  places  where  the  micro- 
filariae are  periodic  and  the  transmitting  mosquitoes  are  nocturnal 
this  should  be  perfectly  possible,  although  in  such  localities  as 
the  Philippines  and  Samoa,  where  the  intermediate  host  is  largely 
diurnal,  it  would  present  almost  insuperable  difficulties.  In 
places  where  Filaria  is  abundant  and  mosquitoes  are  not  ex- 
terminated the  carrying  at  night  of  a  bottle  of  disinfectant,  as 
alcohol  or  dilute  lysol,  for  immediate  application  to  mosquito 
bites  would  be  well  worth  while. 


Other  Species  of  Filaria 

There  are,  as  previously  stated,  a  number  of  other  species  of 
Filaria  which  inhabit  the  human  body.  Filaria  (or  Acantho- 
cheilonema)  perstans  is  extremely  common  in  the  natives  through- 
out Central  Africa  and  also  in  parts  of  northern  South  America; 


308  FILARI.E  AND  THEIR  ALLIES 

it  is  confined  to  regions  of  heavily  forested  tropical  swamps. 
In  some  districts  in  Uganda  it  has  been  found  in  90  per  cent  of 
the  inhabitants.  The  microfilariae  of  this  species  (Fig.  124B) 
are  smaller  than  those  of  F.  hancrofti,  have  a  blunt  tail  and 
lack  the  sheath  which  is  so  characteristic  of  F.  hancrofti.  Fur- 
thermore they  show  no  tendency  to  disappear  periodically  from 
the  peripheral  vessels.  The  adult  worm,  which  has  rarely  been 
found,  is  smaller  than  F.  hancrofti  (about  three  inches  in  length) 
and  occurs  in  the  connective  tissue  of  the  abdominal  and  peri- 
cardial cavities.  The  normal  transmitting  agent,  probably  some 
species  of  mosquito,  is  not  certainly  known.  No  disease  symp- 
toms which  can  be  correlated  with  the  presence  of  the  parasite 
have  yet  been  demonstrated. 

Another  species,  F.  juncea  (demarquaii),  of  which  the  larva 
(Fig.  124D)  is  small  and  without  a  sheath,  as  in  F.  perstans,  but 
with  a  sharp  tail,  occurs  in  the  West  Indies  and  northern  South 
America.  It  is  not  known  to  cause  any  diseased  conditions. 
The  adults  live  in  the  mesenteric  tissues.  In  many  Indians  in 
British  Guiana  F.  perstans  and  F,  juncea  occur  together  in  the 
blood,  and  in  some  cases  the  presence  of  F.  hancrofti  compli- 
cates the  matter  still  more. 

F.  magalhaesi  is  another  species  about  which  very  little  is 
known.  A  pair  of  adult  worms  were  found  only  once,  in  the 
heart  of  a  child  in  Rio  de  Janeiro.  They  were  of  unusually  large 
size,  the  female  measuring  over  six  inches  in 
length  and  the  male  about  three  and  a  half 
inches.  Nothing  is  known  of  the  life  history 
or  pathological  effects. 

The   Lea  Worm.  —  Of  somewhat   different 
nature  from  the  above  species  of  Filaria  is  F. 
loa  or  Loa  loa  (Fig.  128),  a  parasite  found  on 
Fig.  128.     Adult  ^j^^  ^^g^  ^^^g^  q£  Africa,  especially  in  Congo, 

loa    worms,     female  _  . 

(9)  and  male  {$).  which,  as  an  adult,   creeps  in  the  connective 

Looi's'f '''^'  ^'^^^''  ^iss^e  ^f  i^^  ^ost  just  under  the  skin.  The 
female  varies,  probably  with  age,  from  two  to 
two  and  one-half  inches  in  length,  and  is  semi-transparent  and  very 
slender.  The  male  resembles  the  female,  but  is  only  from  one  to 
one  and  one-half  inches  in  length.  Both  sexes  are  characterized 
by  numerous  irregularly  distributed  pimple-like  elevations  of  the 
skin.     The  loa  worm  shows  a  special  preference  for  the  connective 


LOA  WORM 


309 


tissue  in  and  about  the  eyes,  but  may  also  be  found  creeping 
under  the  skin  of  fingers,  breast,  back,  etc.  A  loa  is  said  to  travel 
at  the  rate  of  about  an  inch  in  two  minutes,  and  to  become 
especially  active  in  the  presence  of  direct  warmth  on  the  skin, 
as  before  a  fire.  The  migration  of  the  worms  causes  itching  and 
a  "  creeping  "  sensation,  and  in  some  unexplained  way  gives  rise 
to  temporary  swellings,  from  half  an  inch  to  four  inches  in  diame- 
ter, known  locally  as  "  Calabar  swellings."  These  swellings 
may  shift  their  position  an  inch  or  more  a  day,  and  may  disap- 
pear to  reappear  somewhere  else.  Thi^  relation  of  Loa  to  Cala- 
bar swellings  has  not  been  definitely  proved  but  there  is  strong 
evidence  for  it.  In  one  case  Manson  succeeded  in  finding 
great  numbers  of  microfilariae  of  Loa  in  lymph  taken  from  one 
of  these  swellings,  a  fact  which  gives  color  to  Hanson's  hypothe- 
sis that  the  swellings  might  be  due  to  the  emission  of  larvae  from 
the  parent  worm  into  the  connective  tissue.  The  larvae  of  the 
parasite  (Fig.  124C),  very  closely  resembling  the  microfilariae 
of  F.  hancrofti,  occur  in  the  blood  in  great  numbers,  but  they 
have  a  periodicity  di- 
rectly opposite  to  that 
of  the  latter  species  in 
that  they  swarm  in  the 
peripheral  blood  in  the 
daytime  and  withdraw 
to  the  larger  vessels  at 
night.  The  living 
larvae  of  the  two  species 
cannot  readily  be  dis- 
tinguished from  each 
other   in    fresh   blood, 

1     J.  •_  J   • J  ^«  J  ^4.„,'    ^j  Fig.  129.    Comparison  of  killed  and  stained  speci- 

but  m  dried  and  Stamed  mens  of  M^crofilar^a  bancrofti  and  mf,  loa.     A    mf. 

preparations    the    dead  hancrofti,  —  note  graceful  curves;  B,  mf.  loa,  —  note 

oro-ani^rYmpflnPnmlvhp  irregular  scrawl-like  curves;    C,  tails  of  m/.  Zoa;    D, 

organisms  can  easny  Oe  ^^^^  ^^  ^^  hancrofti.     (After  Manson.) 

identified.     The  micro- 

filaricB  hancrofti  are  found  lying  in  smooth  graceful  curves  (Fig. 
129 A),  while  the  microfilarice  loa  die  in  ungraceful  and  irregular 
scrawl-like  positions  (Fig.  129B),  with  the  tail  nearly  always 
sharply  turned  back  (Fig.  129C). 

There  is  much  evidence  that  the  intermediate  hosts  of  L.  loa 
are  mangrove  flies  of  the  genus  Chrysops,  which  belong  to  the 


B 


310  FILARIiE  AND  THEIR  ALLIES 

horsefly  family,  Tabanidse,  and  resemble  our  deerflies  (see  p.  489 
and  Fig.  227).  Leiper  succeeded  in  obtaining  a  development  of 
microfilaria  loa  in  two  different  species  of  Chrysops.  In  recent 
investigations  in  a  heavily  infested  district  of  Africa,  Kleine 
found  over  five  per  cent  of  600  Chrysops  infected  with  larval  filarise, 
which  he  took  to  be  Loa  loa.  The  worms  were  found  developing 
in  the  fatty  connective  tissue  surrounding  the  tracheae  in  the 
abdomen  of  the  insects  and  later  making  their  way  forward  toward 
the  proboscis.  In  two  cases  larvse  were  induced  to  emerge  from 
the  fly's  proboscis  into  a  few  drops  of  salt  solution.  That  these 
worms  were  really  the  larvse  of  L.  loa  is  entirely  probable,  but 
there  is  no  definite  proof  of  it. 

The  development  of  the  parasites  after  they  have  been  re- 
turned to  a  human  body  is  extremely  slow,  in  fact  the  evidence 
indicates  that  full  sexual  maturity  is  not  reached  for  a  number  of 
years.  The  length  of  life  of  the  worms  is  unusual;  there  are 
cases  recorded  in  which  these  parasites  were  abstracted  from 
patients  who  had  been  away  from  endemic  regions  for  ten  or  15 
years.  Microfilariae  are  not  invariably  found  in  the  blood  of 
infected  persons.  Children,  especially,  are  prone  to  infection 
with  the  creeping  worms,  usually  sexually  immature,  without 
having  any  larvae  in  their  blood.  Even  sexually  mature  para- 
sites apparently  do  not  liberate  larvae  constantly. 

Surgical  removal  of  the  parasites  when  they  present  themselves 
in  the  eye  or  subcutaneous  tissue  is  the  only  remedy  so  far  known. 
Many  of  the  parasites  probably  do  not  expose  themselves  at  all, 
but  remain  in  the  deeper  tissues  and  organs  of  the  body.  When 
they  die  in  the  tissues  they  probably  become  calcified  as  do  the 
adults  of  other  filariae. 

Onchocerca  volvulus.  —  Closely  related  to  the  filariae  is 
another  parasite  of  the  subcutaneous  connective  tissue,  Oncho- 
cerca volvulus.  It  occurs  over  a  large  portion  of  the  west  coast 
and  central  portion  of  Africa.  Three  cases  of  infection  with  the 
same  or  a  closely  alhed  species  has  recently  been  reported  by 
Th6z6  from  French  Guiana.  The  adult  female  is  several  inches 
in  length,  and  slender  as  a  hair;  the  male  is  stouter,  and  little 
over  an  inch  in  length.  The  adults  lie  in  couples  in  fibrous  tumors 
which  can  be  seen  readily  under  the  skin.  The  tumors  vary  in 
size  from  about  one  cm.  (|  of  an  inch)  in  diameter  to  the  size 
of  a  pigeon's  egg,  and  are  found  most  commonly  on  the  hip, 


GUINEA-WORM 


311 


sides  of  the  chest  and  upper  part  of  the  back,  and  sometimes 
in  the  arm  and  knee  pits  and  on  other  parts  of  the  body.  Each 
sweUing  consists  of  dense  fibrous  tissue  in  which  several  pairs  of 
parasites  are  imbedded,  and  contains  small  cystlike  spaces  into 
which  project  the  posterior  end  of  the  male 
with  its  copulatory  organs,  and  the  anterior 
end  of  the  female  with  its  vaginal  opening. 
These  cystlike  spaces  are  usually  swarming 
with  sheathless  microfilariae.  The  latter  are 
believed  by  some  authors  to  leave  the  tumors 
and  to  find  their  way  ultimately  to  the  blood- 
vessels, whence  they  can  be  liberated  by  some 
blood-sucking  insect.  The  intermediate  host 
is  unknown,  but  the  stable-flies,  Stomoxys,  and 
tsetse  flies,  Glossina,  have  been  suspected. 
The  tumors  are  of  long  duration  in  man,  and 
in  some  adults  are  said  to  have  been  present 
since  childhood.  It  is  significant  that  prac- 
tically all  cases  of  elephantiasis  in  the  Welle 
district  of  Congo,  where  Filaria  bancrofti  is  said 
not  to  occur,  are  accompanied  by  infection 
with  Onchocerca  volvulus.  Recently  Robles 
has  described  Onchocerca  ccecutiens  causing 
subcutaneous  nodules  on  the  heads  of  natives 
in  parts  of  Guatemala,  and  suspects  certain 
species  of  Simulium  as  carriers. 

The  Guinea-worm.  Another  connective 
tissue  parasite,  more  distantly  related  to  the 
filariae,  is  the  guinea-worm,  Dracunculus  medi- 
nensis  (Fig.  130).  This  is  a  frequent  parasite 
in  many  parts  of  tropical  Asia  and  Africa  and 
has  been  known  for  a  very  long  time.  The  Fig.  130.  Guinea- 
"  fiery  serpents  "  which  molested  the  Israelites  Z^neL^'le^u 
by  the  Red  Sea  and  were  mentioned  by  Moses  Natural  size.  (After 
were  probably  guinea-worms.  These  parasites  ^^^^^kart.) 
creep  in  the  deeper  layers  of  the  subcutaneous  tissue  where  they 
can  be  more  readily  felt  than  seen,  but  the  females  always  come 
to  the  surface  of  the  skin  to  give  birth  to  the  myriads  of  wriggling 
young. 

The  adult  female  worm,  which  is  the  only  sex  certainly  known, 


312 


FILARIiE  AND  THEIR  ALLIES 


may  attain  a  length  of  four  feet  or  more,  though  the  average 
length  is  about  three  feet,  while  the  diameter  is  less  than  jV  of  an 
inch.  The  body  is  smooth,  cylindrical  and  milky-white  in  color, 
with  the  tip  of  the  tail  sharply  hooked.  The  male  worms  are 
believed  to  be  much  smaller  than  the  females.  When  ready  to 
bring  forth  her  young,  the  guinea-worm  is  instinctively  at- 
tracted to  the  skin,  especially  to  such  parts  as  are  likely  to,  or 
frequently  do,  come  in  contact  with  cold  water,  such  as  the 
arms  of  women  who  wash  clothes  at  a  river's  brink,  or  the  legs 
and  backs  of  water-carriers.  The  worm  pierces  the  lower  layers 
of  the  skin  with  the  front  end  of  her  body  and  the  outer  layers 
of  the  skin  form  a  blister  over  the  injured  spot.     The  blister 

eventually  breaks,  revealing  a 
shallow  ulcer,  about  as  large 
as  a  dime,  with  a  tiny  hole  in 
the  center.  When  the  ulcer  is 
douched  with  water  a  milky 
fluid  is  exuded  directly  from 
the  hole  or  from  a  very  deli- 
cate, transparent  projected 
structure  which  is  a  portion 
of  the  worm's  uterus.  This 
fluid  is  found  to  contain  hordes 
of  tiny  coiled  larvse  with  char- 
acteristic straight  projecting 
tails.  The  larvse  (Fig.  131)  are 
from  0.60  to  0.75  mm.  (about  gV 
of  an  inch)  in  length.  An  hour  or  so  later  a  new  washing  with  cold 
water  will  bring  forth  a  fresh  ejection  of  larvse  and  so  on  until  the 
supply  is  exhausted,  a  little  more  of  the  uterus  being  extruded  each 
time.  After  each  ejection  of  the  larvse  the  protruded  portion  of  the 
uterus  dries  up,  thus  sealing  in  the  unborn  larvse.  This  process 
can  be  looked  upon  only  as  a  wonderful  adaptation  for  the  pres- 
ervation of  the  race.  As  we  shall  presently  see,  the  tiny  larvse 
utilize  various  species  of  Cyclops  (Fig.  132),  small  fresh-water 
crustaceans,  as  intermediate  hosts.  If  the  larvse  were  not  de- 
posited in  water,  or  if  they  were  all  poured  at  once  into  any  bit 
of  water  with  which  the  skin  of  the  host  came  in  contact,  the 
chance  of  their  reaching  a  suitable  Cyclops  would  be  very  small. 
The  result  would  usually  be  family  suicide  and  eventually  race 


Fig.  131.  Cross  section  of  guinea- 
worm  showing  uterus  filled  with  em- 
bryos.     X  about  30.     (After  Leuckart.) 


GUINEA-WORM   IN  CYCLOPS  313 

suicide.  The  repeated  birth  of  a  Hmited  number  of  progeny 
each  time  the  skin  of  the  host  comes  in  contact  with  water  is 
therefore  a  successful  solution  to  a  problem  which  to  a  blind 
burrowing  unmeditative  worm  must  otherwise  present  insuper- 
able difficulties.  When 
all  her  young  have  been 
deposited,  under  the  stim- 
ulus of  contact  with  water, 
the  parent  worm  shrivels 
and  dies  and  is  soon  ab- 
sorbed by  the  tissues  on 
which  she  formerly  preyed 
and  through  which  she 
roamed. 

The  embryo  worms, 
safely  deposited  in  water, 
unroll  themselves  and  be-      fig.  132.    Cydops  sp.  (?),  some  species  of 

gin    to    swim    about    in    a    which  serve  as  intermediate   hosts  of   guinea- 
r     1  •  T        i       ii  worms.      X  about  25. 

fashion  pecuhar  to  them- 
selves. Their  bodies  are  somewhat  flattened  and  they  have  a 
slender  tail.  They  swim  by  a  few  quick  sculling  motions  of  the 
tail,  followed  by  a  pause,  then  a  few  more  strokes,  etc.,  in  the 
manner  of  a  tadpole.  In  turbid  water  they  remain  alive  for 
two  or  three  weeks  but  eventually  perish  unless  they  come  in  con- 
tact with  a  Cyclops,  into  the  body  of  which  they  make  their  way. 

They  usually  enter  by  way  of  the  mouth,  sometimes  as  many 
as  six  or  ten  entering  a  single  Cyclops.  In  a  day  or  two  they 
leave  the  stomach  of  Cyclops  and  enter  the  body  cavity.  In 
spite  of  the  relatively  large  size  of  the  worms  the  crustaceans 
seem  to  feel  very  little  inconvenience,  and  seldom  succumb 
even  to  very  heavy  infection. 

The  young  guinea-worms  become  fully  developed  in  Cyclops 
in  from  four  to  six  weeks,  according  to  the  temperature,  mean- 
while having  undergone  one  and  perhaps  two  moults.  They  are 
then  about  one  mm.  {-^  of  an  inch)  in  length,  and  ready  to  in- 
fect a  new  host.  Entrance  to  the  new  host  is  probably  accom- 
plished by  the  accidental  drinking  of  a  Cyclops  with  unfiltered 
water.  The  female  worms  become  adult  in  their  new  host  in 
about  a  year  so  the  larvae  can  again  be  deposited  at  about  the 
time  that  Cyclops  becomes  abundant. 


314  FILARI.E  AND  THEIR  ALLIES 

The  guinea-worm,  though  annoying  and  to  one  of  fine  sensi- 
bihties  extremely  disgusting,  is  not  in  any  way  dangerous  if  not 
interfered  with.  Should  she  come  to  an  untimely  end,  however, 
or  fail  to  pierce  the  skin,  she  may  give  rise  to  troublesome  ab- 
scesses, though  more  often  the  body  becomes  calcified  and  may 
be  felt  for  years  as  a  hard  twisted  cord  beneath  the  skin.  The 
crude  method  of  abstraction  of  the  worm  which  is  frequently 
practiced  is  the  chief  source  of  danger  from  infection  with  it. 
This  extraction  consists  in  winding  out  the  extruded  part  of  the 
worm  around  a  stick,  drawing  it  forth  a  little  further  each  day. 
Sometimes  this  method  is  successful  but  frequently  it  results  in 
the  snapping  in  two  of  the  worm  beneath  the  skin,  and  the 
consequent  liberation  into  the  tissues  of  thousands  of  young 
worms  with  the  fluid  contents  of  the  uterus.  This  gives  rise 
to  inflammation,  fever,  abscesses  and  even  death  from  blood- 
poisoning. 

A  much  more  effective  and  rational  method  of  treatment  is 
to  bathe  the  part  of  the  body  occupied  by  a  mature  worm  at 
frequent  intervals  until  she  has  emptied  her  uterus,  a  process 
which  takes  two  or  three  weeks.  When  the  birth  of  embryos 
ceases,  gentle  pulling  is  likely  to  bring  the  worm  forth,  but  if 
not  her  body  is  quickly  absorbed  by  the  tissues.  A  more  re- 
cent and  quicker  method  of  dealing  with  a  guinea-worm  is  to 
inject  her  body,  or  the  tissue  in  which  she  is  coiled,  with  a  very 
weak  solution  of  bichloride  of  mercury.  This  kills  her  and  usu- 
ally makes  her  extraction  easy  after  a  few  hours.  Promising 
results  have  recently  been  obtained  by  arsenobenzol  injections 
into  the  host. 

Prevention  of  guinea-worm  infection  consists  obviously  in 
keeping  drinking  water  clear  of  Cyclops,  or  in  thoroughly  filtering 
it,  or,  if  these  measures  are  impracticable,  in  preventing  infected 
persons  from  bathing  in  or  otherwise  contaminating  rivers  or 
other  bodies  of  water  from  which  drinking  water  may  be  taken. 
It  has  been  suggested  that  portable  steam  generators  be  used  to 
heat  the  water  in  wells,  water  holes,  etc.,  in  which  infected 
Cyclops  live,  since  these  crustaceans  succumb  at  a  slightly  ele- 
vated temperature.  Addition  of  small  quantities  of  potash  to 
water  is  also  effective  in  destroying  Cyclops.  The  difficulty 
connected  with  an  attempt  to  exterminate  Cyclops  locally  is 
that  the  eggs  resist  desiccation  and  are  blown  about  freely  by 
the  wind,  so  that  a  new  colony  is  likely  to  spring  up  at  any 
time. 


CHAPTER  XVIII 
LEECHES 

The  annelids  as  a  group  are  not  of  such  primary  importance 
as  parasites  as  are  the  two  other  great  groups  of  ''  worms." 
In  fact  only  one  class,  the  Hirudinea  or  leeches,  contain  species 
which  are  parasitic  on  the  higher  animals. 

No  boy  who  has  ever  experienced  the  unbounded  delights  of 
hanging  his  clothes  on  a  bush  and  immersing  his  naked  body 
for  a  swim  in  a  muddy-bottomed  river  or  pond  is  unfamiliar 
with  leeches  or  "  bloodsuckers."  Still  more  familiar  with  them 
is  any  tourist  who  has  journeyed  on  foot  through  the  jungles  of 
Ceylon  or  Sumatra,  or  any  explorer  who  has  walked  through 
the  warm  moist  valleys  of  the  Himalayas  or  Andes,  and  who  has 
been  attacked  by  hordes  of  bloodthirsty  land-leeches  which  in- 
fest these  places.  Nor  is  it  likely  that  the  thirsty  traveler  in 
North  Africa  or  Palestine  who  stops  to  gulp  a  few  mouthfuls  of 
water  from  a  pool  or  stream  and  who  accidentally  inbibes  one  of 
the  leeches  which  infest  such  waters  will  not  always  remember 
the  bleeding  and  unpleasant  sensations,  and  perhaps  dangerous 
symptoms,  which  follow  the  settlement  of  the  leech  in  the  mouth 
or  nasal  passages. 

General  Anatomy.  —  The  leeches  are  segmented  worms  be- 
longing to  the  phylum  Annelida,  in  company  with  earthworms, 
kelp  worms,  etc.  They  are  distinguished  from  other  annelids 
by  the  absence  of  any  bristle-like  outgrowths  from  the  body 
(setse)  and  by  the  presence  of  two  suckers,  one  at  the  mouth  for 
sucking  food,  and  a  large  one  at  the  posterior  end  for  adhering 
to  surfaces.  The  rings  of  the  body  as  seen  on  the  surface  do  not 
correspond  to  true  segments  of  the  body  as  they  do  in  other 
annelids;  there  are  several  rings  to  most  of  the  segments.  The 
bodies  of  leeches  are  extremely  elastic,  and  can  be  stretched  at 
will  to  several  times  the  contracted  length.  In  fact  the  usual 
method  of  locomotion,  other  than  an  undulating  mode  of  swim- 
ming, is  by  alternately  expanding  and  contracting  the  body, 

315 


316  LEECHES 

adhering  first  by  the  large  posterior  sucker,  then  by  the  smaller 
oral  sucker  and  so  forth. 

Nearly  all  leeches  feed  exclusively  on  blood.  The  digestive 
tract  (Fig.  60C,  p.  197)  is  pecuHar  in  that  the  oesophagus  is  sup- 
plied with  a  series  of  " crops"  or  side  pockets  in  which  blood  can 
be  stored  up  as  a  reserve  supply  to  be  gradually  drawn  back  into 
the  stomach  and  intestine  and  digested  as  needed.  Since  some 
leeches  can  fill  up  with  three  times  their  own  weight  in  blood, 
and  can  live  on  this  supply  for  a  year  or  more,  meals  are  few  and 
far  between.  The  saliva  of  the  leech  has  the  power  of  prevent- 
ing the  coagulation  of  blood,  and  therefore  blood  continues  to 
flow  for  some  time  after  the  leech  has  "  got  his  fill  "  and  let  go. 
Like  other  annelids,  leeches  have  a  true  blood  system  and  a 
series  of  nephridia,  little  coiled  tubes,  a  pair  in  each  segment, 
which  function  as  primitive  kidneys.  There  are  no  special  gills 
or  other  respiratory  organs;  oxygen  is  absorbed  directly  through 
the  skin  which  is  constantly  kept  moist. 

Leeches  are  hermaphroditic,  i.e.,  both  sexes  are  represented 
in  the  same  individual,  but  the  egg  of  one  leech  is  always  ferti- 
lized by  a  sperm  from  another.  In  most  leeches  the  eggs  are 
deposited  in  a  stiff  mucous  cocoon  which  is  secreted  by  a  por- 
tion of  the  body.  When  the  eggs  are  laid  the  cocoon  is  slipped 
over  the  head  like  a  jersey,  the  ends  closing  together  to  form 
a  capsule.  After  a  little  manipulation  with  the  oral  sucker  the 
mother  leech  imbeds  the  cocoon  in  moist  soil,  near  the  edge  of 
water  in  the  case  of  aquatic  species. 

Importance  as  Parasites.  —  The  ordinary  pond  and  river 
leeches  which  adhere  to  bathers  are  of  little  or  no  economic  im- 
portance as  human  parasites.  Of  these  the  well-known  medici- 
nal leeches,  Hirudo,  used  for  sucking  out  infections  or  bad 
blood,  are  the  best  known  examples.  They  are  furnished  with 
powerful  suckers  and  sharp-pointed  pincer-like  jaws,  and  can 
therefore  easily  penetrate  the  skin  and  suck  blood  from  any  part 
of  the  surface  of  the  body.  They  can  usually  be  persuaded  to 
release  their  hold  when  removed  from  water. 

With  the  weak-jawed  members  of  the  genera  Limnatis  and 
Hcemopis,  commonly  known  as  horse  leeches,  it  is  quite  dif- 
ferent. These  animals  seek  to  penetrate  the  natural  openings 
of  the  body  and  fasten  themselves  to  the  mucous  membranes, 
especially  in  the  mouth  and  nasal  cavities,  where  they  may  cause 


LEECHES  IN  MOUTH  OR  NOSE  317 

such  extensive  bleeding  as  to  bring  about  the  death  of  the  host. 
Of  perhaps  even  greater  importance,  because  more  difficult  to 
avoid,  are  the  bloodthirsty  land-leeches  which  have  already  been 
mentioned  as  infesting  many  tropical  countries.  Leeches  serve 
as  intermediate  hosts  for  many  species  of  trypanosomes  of  fishes 
and  other  aquatic  animals,  and  it  is  not  impossible  that  they  may 
be  found  to  transmit  some  species  to  man. 

Leeches  in  the  Mouth  or  Nose.  —  The  leeches  which  habitu- 
ally settle  themselves  in  the  mouth  or  nasal  cavities  of  men  or 
animals  are  inhabitants  of  muddy-bottomed  ponds,  ditches, 
reservoirs,  troughs,  etc.,  and  enter  the  mouth  or  nose  of  their 
host  while  he  is  drinking.  According  to  Masterman,  leeches  of 
the  species  Limnatis  nilotica  become  so  abundant  in  northern 
Palestine  in  late  summer  and  autumn  that  almost  every  horse 
and  mule  passing  through  these  parts  has  a  bleeding  mouth. 
The  Nile  leech,  Limnatis  nilotica,  is  the  most  plentiful  species 
around  the  shores  of  the  Mediterranean,  but  leeches  of  the 
genus  Hoemopis,  with  similar  habits,  also  occur  over  a  large  part 
of  Europe.  Troublesome  aquatic  leeches  have  been  reported 
by  travelers  in  the  lake  regions  of  central  Africa  also,  and  in 
some  other  warm  countries,  especially  Formosa. 

The  young  leeches,  which  are  usually  the  ones  which  enter 
the  mouth  or  nose  during  drinking,  are  only  a  fraction  of  an  inch 
in  length,  but  the  adults  reach  a  length  of  several  inches.  The 
average  length  of  Limnatis  nilotica  is  about  one  inch  or  less. 

A  person  while  drinking  from  infected  pools,  especially  in 
dusk  or  at  night,  is  very  likely  to  suck  in  one  or  more  of  these 
leeches.  During  the  process  of  swallowing  the  parasites  attach 
themselves  to  the  walls  of  the  mouth  or  pharynx  and  may  mi- 
grate into  the  nose  or  larynx.  Seldom,  if  ever,  are  the  leeches 
completely  swallowed,  and  even  if  they  should  reach  the  stomach 
they  would  probably  be  killed  at  once  and  digested.  It  is  a 
peculiar  and  indeed  unfortunate  fact  that,  while  the  leeches 
which  attack  the  surface  of  the  body  fill  with  blood  and  then 
let  go,  those  which  settle  on  the  mucous  membranes  keep  their 
hold  for  days  or  weeks,  though  they  shift  their  positions,  leaving 
the  old  bites  to  continue  bleeding.  As  already  stated,  the  loss 
of  blood  from  the  wounds  made  by  the  leeches  is  often  sufficient 
to  cause  an  extreme  or  even  fatal  anemia,  though  the  hemor- 
rhages of  clear  blood  are  never  great  in  quantity  at  any  one  time. 


318  LEECHES 

The  blood  flows  out  of  the  nose  or  into  the  throat  or  trachea,  in 
the  latter  cases  being  constantly  "  hawked  "  up.  Masterman 
describes  the  case  of  a  man  in  Palestine,  attacked  by  leeches,  who 
for  nearly  a  week  had  been  "  spitting  blood  "  and  had  a  spittoon 
full  of  practically  pure  blood  by  his  side,  every  few  minutes  adding 
more.  His  lips  were  blue,  and  he  was  unable  to  speak  above 
a  whisper.  Every  few  minutes  he  had  a  short  cough.  Often 
when  the  leech  is  attached  in  the  larynx  beside  the  vocal  cords, 
the  body  flops  back  and  forth  during  breathing,  and  has  been 
known  to  cause  asphyxiation  by  blocking  the  trachea.  Cases  are 
on  record  where  leeches,  having  fallen  into  one  of  the  bronchi, 
have  died  and  disintegrated,  and  thus  caused  destructive  bac- 
terial infections  to  set  in.  The  presence  of  leeches  in  the  mucous 
membranes  is  often  accompanied  by  severe  headaches.  Some- 
times leeches  which  have  settled  in  the  nose  have  the  revolting 
habit  of  protruding  themselves  from  the  nostrils  and  allowing  a 
portion  of  the  body  to  wander  over  the  upper  lip.  They  are, 
however,  so  elusive  that  they  can  be  captured  only  with  great 
difficulty. 

The  treatment  employed  for  leech  infestations  of  the  nose 
or  mouth  varies  greatly  in  different  countries.  According  to 
Masterman  the  natives  of  Palestine  transfix  the  leech,  if  within 
reach,  with  a  thorn  from  a  native  tree,  and  muleteers  extract 
leeches  from  mules'  mouths  with  packing  needles.  When  the 
parasite  is  beyond  reach  of  this  transfixing  process  these  people 
smear  some  of  the  thick  deposit  which  collects  in  their  tobacco 
pipes  on  a  splinter  of  wood  and  endeavor  to  touch  the  leech  with 
it;  this  is  said  to  cause  the  leech  to  lose  its  hold.  Masterman 
found  the  most  successful  means  of  removing  a  leech  to  be  either 
to  seize  it  with  a  suitable  forceps,  or  to  paralyze  it  with  cocaine. 
Much  difficulty  is  often  experienced  in  seizing  the  writhing, 
slippery  creature  with  a  pair  of  forceps  even  when  it  can  be  seen 
clearly  with  a  mouth  mirror,  partly  on  account  of  the  spasmodic 
contractions  of  the  larynx  and  the  frequent  coughing.  The 
paralyzing  of  the  worms  with  cocaine  is  a  very  successful  method ; 
it  is  done  by  touching  the  worm  with  a  30  per  cent  cocaine  solu- 
tion on  a  bit  of  cotton.  The  worm  becomes  paralyzed  in  a  few 
minutes  after  being  touched,  and  releases  its  hold.  To  avoid 
the  possibility  of  the  leech  falling  into  the  trachea  the  patient  is 
made  to  lie  on  a  couch  with  his  head  hanging  over  the  edge. 


LAND-LEECHES  319 

Land-leeches.  —  Of  perhaps  greater  importance,  because  far 
less  easy  to  avoid,  are  the  attacks  of  the  land-leeches  of  many 
tropical  countries.  These  leeches  are  found  in  Ceylon,  Japan, 
Sumatra,  Philippine  and  East  Indian  Islands,  Australia,  and  the 
humid  mountain  meadows  of  the  Himalayas  in  India  and  of  the 
Andes  in  South  America.  Sir  J.  Emerson  Tennent  in  his  book 
on  ''The  Natural  History  of  Ceylon"  writes  as  follows:  "Of 
all  the  plagues  which  beset  the  traveler  in  the  higher  grounds  of 
Ceylon  the  most  detested  are  the  land-leeches,  Hcemadipsa 
ceylonica.  They  are  not  frequent  in  the  plains,  which  are  too 
hot  and  dry  for  them,  but  among  the  rank  vegetation  of  the 
lower  hill  country,  which  is  kept  damp  by  frequent  showers, 
they  are  found  in  tormenting  profusion.  They  are  terrestrial, 
never  visiting  ponds  or  streams.  In  size  they  are  about  an  inch 
in  length  and  as  fine  as  a  common  knitting  needle,  but  they  are 
capable  of  distension  till  they  equal  a  quill  in  thickness  and  at- 
tain a  length  of  nearly  two  inches.  Their  structure  is  so  flexible 
that  they  can  insinuate  themselves  through  the  meshes  of  the 
finest  stocking,  not  only  seizing  on  the  feet  or  ankles,  but  ascend- 
ing to  the  back  or  throat,  and  fastening  on  the  tenderest  parts 
of  the  body.  In  order  to  exclude  them  the  coffee  planters  who 
live  among  these  pests  are  obUged  to  envelope  their  legs  in 
"  leech  garters  "  made  of  closely  woven  cloth.  The  natives 
smear  their  bodies  with  oil,  tobacco  ashes  or  lemon  juice,  the  last 
serving  not  only  to  stop  the  flow  of  blood,  but  also  to  expedite 
the  healing  of  the  wounds.  In  moving,  the  land-leeches  have 
the  power  of  planting  one  extremity  on  the  earth  and  raising  the 
other  perpendicularly  to  watch  for  their  victim.  Such  is  their 
vigilance  and  instinct  that,  on  the  approach  of  a  passerby  to  a 
spot  which  they  infest,  they  may  be  seen  amongst  the  grass  and 
fallen  leaves  on  the  edge  of  a  native  path,  poised  erect,  and  pre- 
pared for  their  attack  on  man  and  horse.  Their  size  is  so  in- 
significant and  the  wound  they  make  is  so  skillfully  punctured 
that  both  are  generally  imperceptible,  and  the  first  intimation  of 
their  onslaught  is  the  trickling  of  the  blood  or  a  chill  feeling  of 
the  leech  when  it  begins  to  hang  heavily  on  the  skin  from  being 
distended  with  its  repast.  Horses  are  driven  wild  by  them  and 
stamp  the  ground  in  fury  to  shake  them  from  their  fetlocks,  to 
which  they  hang  in  bloody  tassels.  The  bare  legs  of  the  palankin 
bearers  and  coolies  are  a  favorite  resort,  and  as  their  hands  are 


320 


LEECHES 


too  much  engaged  to  pull  them  off  the  leeches  hang  like  bunches 
of  grapes  round  the  ankles.  Both  Marshall  and  Davy  mention 
that  during  the  march  of  troops  in  the  mountains  when  the 
Kandyans  were  in  rebellion  in  1818,  the  soldiers,  and  especially 
the  Madras  Sepoys,  with  the  pioneers  and 
coolies,  suffered  so  severely  from  this  cause 
that  numbers  perished. 

One  circumstance  regarding  these  land- 
leeches  is  remarkable  and  unexplained:  they 
are  helpless  without  moisture,  and  in  the  hills 
where  they  abound  at  all  other  times  they 
entirely  disappear  during  long  droughts;  yet 
reappear  instantly  at  the  very  first  fall  of  rain, 
and  in  spots  previously  parched,  where  not  one 
was  visible  an  hour  before,  a  single  shower  is 
sufficient  to  reproduce  them  in  thousands. 
Whence  do  they  reappear!  May  they,  like 
rotifers,  be  dried  up  and  preserved  for  an 
indefinite  period,  resuming  their  vital  activity 
on  the  mere  recurrence  of  moisture?  " 

Similar  reports  come  from  travelers  in  other 
tropical  countries.  Alfred  Wallace  encountered 
land-leeches  in  Sumatra  where  he  found  them 
infesting  the  leaves  and  herbage  by  the  side 
of  the  paths  through  the  forests.  At  the 
approach  of  a  traveler  as  indicated  by  foot- 
steps or  a  rustling  of  leaves,  the  leeches  stretched 
themselves  out  at  full  length  and  attached 
themselves  to  any  part  of  the  passerby  which 
they  happened  to  touch.  Their  presence  and 
FiQ.   133.     Japa-  -^j^g  jQgg  Qf  blood  was  Seldom  felt  during  the 

nese     land-leech,  .  ^         n  •  i  i      i 

Hoemadipsa  japoni-  excitement  of  Walking,  but  a  dozen  or  so  had 
Sft^rwht^  ^  ^  ^^  ^®  picked  off  every  evening.  Dean  C. 
Worcester  in  his  book  on  the  Philippines 
says  "  the  moist  earth  swarmed  with  leeches  which  crawled 
through  my  stockings  and  bit  my  ankles  until  my  shoes  were 
soaked  with  blood."  One  species,  H.  japonica  (Fig.  133),  is 
common  in  parts  of  Japan.  The  land-leech  of  Australia  belongs  to 
a  different  genus,  Philcemon. 

In  any  of  the  localities  infested  by  land-leeches  it  is  advisable 


PROTECTION  FROM  LAND-LEECHES  321 

to  bind  the  feet  and  legs  in  leech-proof  cloth,  this  being  preferable 
to  various  ointments  which  are  supposed  to  discourage  the  leeches 
from  their  meal.  In  a  tropical  cUmate  where  so  many  diseases 
and  unfavorable  conditions  beset  one  on  every  side,  it  is  impor- 
tant to  take  every  precaution  to  keep  in  perfect  health.  The 
loss  of  blood  from  the  attacks  of  leeches,  and  the  portal  given 
for  entrance  of  bacteria  and  other  organisms  in  the  wounds  made 
by  them,  might  make  all  the  difference  between  life  and  death 
in  the  struggle  for  existence  in  these  disease-plagued  chmes. 


PART  III  — ARTHROPODS 

CHAPTER  XIX 

INTRODUCTION  TO  ARTHROPODS 

To  the  average  person  it  is  astonishing  to  learn  that  the  insects 
and  their  alhes,  constituting  the  phylum  Arthropoda,  include 
probably  more  than  four  times  as  many  species  as  all  other 
animals  combined.  In  this  vast  horde  of  animal  forms  are 
included  some  species  which  are  distinctly  valuable  to  the  human 
race,  such  as  bees,  the  silkworm,  the  thousands  of  insects  (Dip- 
tera  and  Hymenoptera)  parasitically  destructive  to  injurious 
species  and  the  predaceous  beetles;  a  great  number  which  are 
indifferent  as  regards  their  economic  importance  serving,  perhaps, 
only  to  arouse  admiration  for  their  beauties  or  disgust  for  their 
loathsomeness;  and  many  which  are  of  great  importance  as 
crop  pests  or  as  annoyers  of  domestic  stock  or  of  man  himself. 
Only  relatively  very  few,  a  mere  handful,  are  injurious  to  man  as 
parasites  or  as  disease  carriers,  but  these  few  are  of  almost  in- 
calculable importance.  As  mere  parasites  the  parasitic  arthro- 
pods are  of  minor  importance,  but  it  is  in  their  capacity  as  inter- 
mediate hosts  of  other  parasites  or  as  mechanical  carriers  of 
disease  germs  that  these  animals  have  to  be  reckoned  with  as 
among  the  foremost  of  human  foes.  Every  arthropod,  para- 
sitic or  otherwise,  which  habitually  comes  in  direct  or  indirect 
contact  with  man  must  be  looked  upon  as  a  possible  disease  car- 
rier. The  role  of  arthropods  in  the  dissemination  of  disease  is  a 
matter  about  which  practically  nothing  was  known  35  or  40 
years  ago.  A  French  physician.  Dr.  Beauperthuy,  in  1853  was 
one  of  the  first  to  express  a  belief  in  the  dissemination  of  various 
diseases  by  mosquitoes  and  in  the  role  of  the  housefly  in  the 
spread  of  pathogenic  organisms.  In  1879  Manson  first  proved 
insects  to  be  intermediate  hosts  of  human  parasites,  in  the  case 
of  Filaria  and  the  mosquito.  Since  that  time  many  of  the  most 
important  human  diseases  have  been  shown  not  only  to  be  trans- 

322 


RELATIONSHIPS  323 

mitted  by  arthropods  but  to  be  exclusively  transmitted  by  certain 
species  or  genera.  In  the  latter  category,  as  far  as  we  know  at 
present,  are  malaria,  by  some  physicians  rated  as  the  most  im- 
portant human  disease;  typhus  fever,  the  unseen  dragon  of  death 
which  hovers  over  every  war  camp  in  the  world;  yellow  fever, 
which  formerly  haunted  South  and  Central  America;  sleeping 
sickness,  the  scourge  of  Central  Africa;  Chagas'  disease  of 
South  America;  relapsing  fever;  Rocky  Mountain  spotted  fever; 
dengue;  phlebotomus  fever;  Japanese  flood  fever;  filarial  dis- 
eases; guinea-worm  infection;  lung  fluke  infection;  some  tape- 
worm infections;  and  others  of  less  importance.  Some  other 
important  diseases,  such  as  kala-azar  and  oroya  fever,  are  be- 
lieved to  be  transmitted  by  arthropods  but  the  transmitting 
agents  have  not  yet  been  discovered. 

There  are  many  other  diseases  which,  although  they  may  be 
transmitted  in  other  ways  also,  are  commonly  disseminated  by 
insects,  often  in  a  more  or  less  mechanical  way.  Such  are  plague, 
tuberculosis,  leprosy  and  others.  In  the  case  of  some  of  these 
diseases,  e.g.,  plague,  the  intestines  of  the  transmitting  arthro- 
pods serve  as  culture  tubes  for  the  disease  germs,  whereas  in 
other  cases,  e.g.,  amebic  dysentery,  the  arthropods  are  merely 
passive  carriers  of  disease  germs  which  adhere  to  their  feet  or 
bodies.  It  is  evident  that  any  insect  may  serve  as  a  disseminator 
of  disease  in  this  mechanical  way  in  direct  proportion  to  the  ex- 
tent that  it  associates  with  man  and  that  its  habits  bring  it  in 
contact  with  disease  germs. 

Relationships.  —  The  insects  and  their  allies,  constituting  the 
phylum  Arthropoda,  are  the  most  highly  organized  of  inverte- 
brate animals,  and  stand  at  the  head  of  their  particular  line  of 
evolution.  They  find  their  nearest  allies  in  the  segmented  worms 
or  annelids,  i.e.,  earthworms,  leeches,  etc.,  but  most  of  them  show 
a  great  advance  over  their  lowly  cousins.  Like  the  annelids 
they  have  a  segmented  type  of  body,  though  in  some  types,  such 
as  the  mites,  all  the  segments  become  secondarily  confluent. 
Like  the  annelids,  also,  the  arthropods  are  protected  by  an  ex- 
ternal skeleton  which  usually  consists  of  a  series  of  horny  rings 
encircling  the  body.  The  most  obvious  distinguishing  character- 
istic of  the  arthropods  is  the  presence  of  jointed  appendages  in 
the  form  of  legs,  mouthparts  and  antennae.  Internally  they  are 
distinguished  from  other  invertebrates  in  that  the  body  cavity, 


324  INTRODUCTION  TO  ARTHROPODS 

SO  conspicuous  in  the  annelids,  has  been  entirely  usurped  by  a  great 
expansion  and  running  together  of  bloodvessels  so  that  in  the 
place  of  the  usual  body  cavity  or  ccelom  there  is  a  large  blood- 
filled  space.  Within  this  space  are  bloodvessels  and  a  so-called 
heart,  which  retained  their  individuality  while  the  other  vessels 
fused. 

Classification.  —  The  phylum  Arthropoda  is  divided  into  five 
classes.  One  of  these,  the  Onychophora,  includes  only  a  single 
genus  of  animals,  Peripatus,  which  is  very  primitive,  and  helps 
to  bridge  the  gap  between  the  more  typical  arthropods  and  the 
annelids.  Peripatus  is  a  free-living  wormlike  animal  and  of  no 
interest  here.  The  remaining  four  classes  are  the  Crustacea, 
Arachnida,  Myriapoda  and  Insecta. 

The  Crustacea,  including  crayfish,  water  fleas,  etc.,  are  pri- 
marily arthropods  of  the  water.  They  are  geologically  of  great 
antiquity  and  among  them  are  the  most  primitive  of  the  typical 
arthropods.  Their  appendages  are  usually  numerous  and,  taking 
the  group  as  a  whole,  show  a  wonderful  range  of  modifications 
for  nearly  every  possible  function.  Crustaceans  breathe  by  gills. 
Although  many  are  parasites  of  aquatic  animals,  none  can  be 
considered  as  parasites  of  man  or  other  land  animals.  In  two 
cases  Crustacea  are  known  to  serve  as  the  intermediate  hosts  of 
human  parasites,  namely  Cyclops  as  a  host  for  the  guinea-worm 
(see  p.  312),  and  the  Japanese  land  crabs  as  the  second  inter- 
mediate hosts  of  the  lung  fluke  (see  p.  222). 

The  Arachnida,  including  spiders,  scorpions,  mites,  etc.,  are 
for  the  most  part  highly  developed  arthropods,  representing  the 
terminus  of  a  separate  line  of  evolution.  They  probably  had  a 
common  origin  with  the  Crustacea,  but  have  become  adapted 
to  terrestrial  life.  The  members  of  this  class  have  four  pairs  of 
legs  as  adults,  two  pairs  of  mouthparts  and  no  antennae.  They 
breathe  by  means  of  invaginations  of  the  body  which  contain 
gills  arranged  like  the  leaves  of  a  book,  whence  the  name  "  book 
lungs."  Some  of  the  higher  arachnids  also  have  a  system  of 
branched  air  tubes  or  tracheae  in  the  body  similar  to  those  found 
in  the  insects  and  myriapods.  Two  orders  of  Arachnida  contain 
parasitic  species,  namely  the  Acarina,  or  mites  and  ticks,  and 
Linguatulina,  or  tongue-worms.     Many  ticks  are  disease  carriers. 

The  Myriapoda,  including  centipedes  and  millipedes,  are 
terrestrial  arthropods  which  breathe  by  tracheae.     The  body  is 


MOUTHPARTS  OF  INSECTS 


325 


furnished  with  a  distinct  head,  followed  by  a  considerable  num- 
ber of  similar  segments,  each  bearing  one  or  two  pairs  of  legs. 
There  is  a  single  pair  of  antennae.  Although  some  of  the  centi- 
pedes are  poisonous,  none  of  the  myriapods  are  parasitic,  nor 
are  any  of  them  known  to  be  disease  carriers. 

The  Insecta,  or  insects,  represent  the  zenith  of  invertebrate 
life.  They  are  terrestrial  arthropods  which,  like  the  myriapods, 
breathe  by  tracheae.  Their  appendages,  however,  are  reduced 
to  one  pair  of  antennae,  two  pairs  of  mouthparts  and  three  pairs 
of  legs  with  usually  the  addition,  if  not  secondarily  lost,  of  two 
pairs  of  wings.  The  wings  are  really  mere  outgrowths  or  folds 
of  the  integument  or  "  skin  "  of  the  insect,  between  the  two  layers 
of  which  are  branches  of  the  tracheae,  represented  by  the  "  veins" 
in  the  wings  of  adult  insects.  There  is  a  fundamental  plan  of  ar- 
rangement of  the  veins  which  is  variously  modified  in  different  in- 
sects, but  absolutely  fixed  in  any  given  species.  The  venation 
of  the  wings  is  often  of  great  value  in  the  identification  of  genera 
or  species  of  insects.  An  insect  is  always  readily  divisible  into 
three  parts,  the  head,  thorax  and  abdomen.  The  head,  in  addi- 
tion to  the  antennae  already  mentioned,  bears  two  compound  eyes 
sometimes  of  relatively  enormous  size,  usually  several  simple  eyes, 
and  the  mouthparts. 

Mouthparts  of  Insects.  —  Incredible  as  it  may  seem  at  first 
thought,  the  mouthparts  of  all  kinds  of  insects,  from  the  simple 
chewing  organs  of  a  grasshopper  to  the  highy  modified  piercing 
and  sucking  organs  of  biting  flies  and  mosquitoes  and  the  great 
coiled  sucking  tube  of  butterflies  and  moths,  are  modiflcations 
of  a  single  fundamental  type.  This  type  is  represented  in  its 
simplest  form  in  the  chewing  or  biting  type,  as  found  in  grass- 
hoppers and  beetles  (Fig.  134).  The  mouthparts  in  these  in- 
sects consist  (1)  of  an  upper  lip  or  labrum  (Fig.  134,  Lbr.); 
(2)  a  lower  lip  or  labium  (Fig.  134,  Lbm.),  really  formed  of  a 
pair  of  organs  fused  together,  each  bearing  a  segmented  appen- 
dage, the  labial  palpus  (Fig.  134,  Lab.  p.);  (3)  a  pair  of  hard, 
horny,  toothed  mandibles  or  jaws  (Fig.  134,  Mand.)  lying  just 
under  the  lower  lip,  which  chew  up  food  by  a  horizontal  instead 
of  vertical  movement;  (4)  a  pair  of  maxillae  (Fig.  134,  Max.), 
lying  between  the  mandibles  and  lower  lip,  each  bearing  a  seg- 
mented appendage  more  or  less  like  those  on  the  lower  hp,  and 
caUed  the  maxillary  palpus   (Fig.   134,   Max.   p.)   and   (5)   the 


326 


INTRODUCTION  TO  ARTHROPODS 


hypopharynx  (Fig.  134,  Hyp.),  a  short  fleshy  organ  lying  in  the 
midst  of  the  other  organs,  and  comparable  in  both  form  and 
function  with  the  tongue  of  vertebrate  animals.  In  addition  to 
these  parts  there  is  a  horny  lining  of  the  upper  lip  and  roof  of 


^^'L-a^'P* 


Lbm. 
Fig.  134.     Simple  mouthparts  of  a  chewing  insect    (Stenopalmatus) ;    Ibr.,  la- 
brum,  or  upper  lip;  mand.,  mandible;  hyp.,  hypopharynx  or  tongue;  max.,  maxilla; 
max.  p.,  maxillary  palpus;  lbm.,  labium  or  lower  lip  (really  a  second  pair  of  maxillse 
fused  together);   lab.  p.,  labial  palpus. 

the  mouth  cavity  known  as  the  epipharynx.  This  structure 
is  usually  closely  associated  with  the  upper  lip,  so  that  the  com- 
bined organ  is  spoken  of  as  the  "  labrum-epipharynx." 

The  extent  of  the  modifications  which  these  mouthparts  may 
undergo  is  wonderful,  especially  in  insects  where  they  are  modi- 
fied for  sucking  or  piercing.  In  the  true  bugs  the  mandibles 
and  maxillse  are  prolonged  into  needle-like  organs,  the  maxillae 
often  armed  with  sawlike  teeth  at  their  tips,  and  the  lower  lip 
is  developed  into  a  thick,  fleshy,  jointed  proboscis,  grooved  on  its 
upper  side  to  form  a  sheath  for  the  piercing  organs  (Fig.  164). 
The  labrum  is  a  short  movable  flap,  and  the  hypopharynx  is  very 
sHghtly  developed.  In  the  Diptera,  which  include  the  mos- 
quitoes, gnats,  blackflies,  tsetse  flies  and  other  biting  flies  as 
well  as  houseflies  and  blowflies,  there  are  several  different  types 


GENERAL  ANATOMY  OF  INSECTS  327 

of  modifications.  In  mosquitoes  the  mouthparts  (Fig.  191)  are 
much  as  in  bugs,  but  the  labrum-epipharynx  and  hypopharynx 
are  also  modified  into  long  piercing  organs,  and  the  latter  is 
fashioned  into  a  true  hypodermic  needle  for  injecting  salivary 
secretions.  In  blackflies  and  tabanids  (Figs.  220  and  225)  the 
parts  are  similar  but  the  piercing  organs  are  shorter  and  more 
bladelike,  resembUng  daggers  rather  than  needles.  In  the 
tsetse  flies  and  stable-flies  (Figs.  220  and  225)  the  lower  lip  itself 
is  the  chief  piercing  organ,  the  labrum-epipharynx  and  hypo- 
pharynx  contained  in  it  being  needle-like  and  capable  of  forming 
a  sucking  tube  by  apposition  with  each  other.  The  mandibles 
and  maxillae  are  much  reduced  or  rudimentary,  but  the  maxillary 
palpi  are  conspicuous,  and  in  tsetse  flies  form  a  perfect  sheath 
for  the  proboscis.  In  the  houseflies  and  their  non-blood-sucking 
allies  the  mouthparts  are  most  modified,  being  all  molded  to- 
gether to  form  a  fleshy  proboscis  especially  fitted  for  lapping 
up  liquid  foods.  In  fieas  the  mouthparts  (Fig.  178)  are  somewhat 
as  they  are  in  the  biting  flies,  but  the  mandibles  are  not  modified 
as  piercing  organs  but  as  protective  flaps,  and  the  sheath  for  the 
piercing  organs  is  formed  from  the  labial  palpi  instead  of  from 
the  labium  or  lower  lip  itself.  The  mouthparts  of  sucking  lice 
(Fig.  171)  are  still  not  thoroughly  understood  but  the  piercing 
and  sucking  organs,  whatever  parts  they  really  represent,  can 
be  retracted  into  a  blind  pouch  under  the  pharynx.  The  mouth 
parts  of  such  insects  as  moths,  bees,  wasps,  etc.,  are  also  remark- 
able examples  of  structural  adaptations,  but  they  do  not  concern 
us  here. 

General  Anatomy.  —  The  digestive  tract  of  insects  (Fig.  135) 
is  often  highly  developed  and  differentiated.  The  blood-sucking 
insects  have  a  muscular  pharynx  in  the  head  which  acts  like  a 
suction  pump.  In  the  bedbug,  for  instance,  the  powerful  muscles 
which  are  used  to  expand  the  pharynx  and  thereby  produce 
suction  occupy  a  considerable  portion  of  the  inside  of  the  head, 
and  the  area  on  top  of  the  head  to  which  they  are  attached  is 
distinctly  visible  on  the  outside.  The  pair  of  salivary  glands 
open  into  the  floor  of  the  pharynx,  but  they  themselves  are 
usually  situated  in  the  thorax.  Often  they  are  very  highly  de- 
veloped. In  the  true  bugs  they  have  connected  with  them 
accessory  salivary  glands,  which  in  some  species  may  serve  at 
least  in  part  as  storage  vats  for  holding  the  secretion  temporarily. 


328 


INTRODUCTION  TO  ARTHROPODS 


In  mosquitoes  (Fig.  189)  the  salivary  glands  consist  of  three 
lobes,  one  lobe  being  noticeably  different  in  appearance  and 
secretion  from  the  others.  The  pharynx  connects  with  the 
stomach  by  a  slender  oesophagus.     Various  means  are  used  by 

blood-sucking  insects  to  increase 
their  capacity.  In  the  bugs 
(Fig.  135)  the  stomach  is  ex- 
tremely distensible  and  serves  as 
a  storage  reservoir.  In  fleas  and 
many  biting  flies  there  is  an  ex- 
pansion of  the  oesophagus  an- 
terior to  the  true  stomach,  called 
the  proventriculus;  in  mosqui- 
toes there  are  capacious  pouch- 
like food  reservoirs  or  outgrowths 
from  the  oesophagus  in  addition 
to  the  proventriculus  (Fig.  189). 
Just  behind  the  true  stomach  at 
the  beginning  of  the  intestine 
there  open  a  number  of  long 
slender  tubes,  the  ''Malpighian 
tubules"  (Fig.  135,  malp.  t.). 
These  are  the  excretory  organs, 
corresponding  to  the  kidneys  of 
vertebrate  animals.  Their  func- 
tion is  to  collect  the  waste 
matter  of  metabolism  from  the 
blood  and  pour  it  into  the  in- 
testine, whence  it  can  ultimately  be  voided  through  the  anus. 
The  length  of  the  intestine  varies,  being  usually  longer  in  vege- 
table-feeding insects  than  in  carnivorous  ones.  It  often  has  a 
marked  expansion,  the  anal  pouch,  at  its  posterior  end. 

The  tracheae  of  insects,  as  already  intimated,  are  really  a  ven- 
tilation system  consisting  of  air  tubes  ramifying  all  through  the 
body  even  to  the  tips  of  the  antennae  and  legs.  They  open  by  a 
series  of  pores  along  the  sides  of  the  insect  known  as  spiracles, 
which  function  as  do  the  nostrils  of  higher  animals.  The  prin- 
ciple of  oil  sprays  for  insects  is  to  form  a  film  of  oil  over  the 
spiracles,  so  that  the  insects  will  suffocate. 

The  nervous  system  of  insects  is  very  highly  developed  for 


ma'p.t. 


rcct. 


Fig.  135.  Digestive  tract  of  a  Re- 
duviid  bug;  ace.  sal.  gl.,  accessory- 
salivary  gland;  conn,  d.,  connecting 
duct  between  salivary  glands;  int.,  in- 
testine; malp.  t.,  malpighian  tubules; 
oes.,  oesophagus;  rect.,  rectum;  sal.  gl., 
salivary  gland.     (Partly  after  Dufour.) 


LIFE  HISTORY  OF  INSECTS  329 

invertebrate  animals.  In  some  species  the  instincts,  especially 
those  connected  with  providing  for  their  offspring,  simulate  care- 
ful and  accurate  reasoning,  and  it  is  difficult  not  to  look  upon 
them  as  animals  endowed  with  a  high  degree  of  intelligence. 

Life  History.  —  As  regards  life  history,  three  different  types 
can  be  recognized  among  insects.  In  the  primitive  order  Thy- 
sanura  alone  there  occurs  "  direct  development "  in  which  the 
newly  hatched  insect  is  nearly  a  miniature  of  its  parent,  and 
merely  increases  in  size.  The  two  common  types  of  development 
are  by  incomplete  and  complete  metamorphosis.  Insects  which 
have  an  incomplete  metamorphosis  are  those  which  differ  more  or 
less  from  their  parents  when  hatched,  but  which  gradually  assume 
the  parental  form  with  successive  moults  or  sheddings  of  the 
skin.  The  young  or  ''  nymphs  "  of  such  insects  invariably  lack 
wings,  and  often  have  other  characteristics  different  from  their 
parents.  In  such  insects  as  lice,  in  which  the  wings  are  absent  in 
the  adult,  there  is  very  little  difference  except  in  size  between 
the  young  and  adult  forms.  Insects  which  have  a  complete 
metamorphosis  are  those  in  which,  as  in  butterflies,  the  newly 
hatched  larva  is  totally  different  from  the  parent,  and  does  not 
gradually  assume  the  parental  form.  Instead,  it  retains  its  worm- 
like larval  characteristics  until  full  grown  and  then  transforms, 
during  a  resting  and  more  or  less  quiescent  period  of  relatively 
short  duration,  into  the  adult  form.  This  transformation,  which 
may  amount  to  nothing  short  of  a  complete  remodeling  of  the 
entire  body  and  all  its  organs,  is  sometimes  accomplished  in  an 
amazingly  short  time.  Many  maggots  transform  into  adult  flies 
in  less  than  a  week,  and  some  mosquito  larvae  transform  into 
perfect  mosquitoes  in  less  than  24  hours. 

The  length  of  life  of  insects  in  the  larval  and  adult  stages 
varies  with  almost  every  species  and  with  environmental  con- 
ditions. The  larval  stage  may  occupy  a  small  portion  of  the 
life,  as  in  the  case  of  many  mosquitoes  and  flies,  or  it  may  con- 
stitute the  greater  part  of  it.  There  are  some  mayflies,  for 
instance,  which  live  the  greater  part  of  two  years  as  larvae  but 
exist  as  adults  not  more  than  a  few  hours.  As  a  rule  male  in- 
sects are  shorter  lived  than  the  females;  the  length  of  life  of  the 
latter  is  determined  by  the  laying  of  the  eggs  —  when  all  the 
eggs  have  been  laid  the  female  insect  has  performed  her  duty 
in  fife  and  is  eUminated  by  nature  as  a  useless  being.     The  result 


330  INTRODUCTION   TO  ARTHROPODS 

is  the  paradoxical  fact  that  ideal  environmental  conditions 
shorten  the  life  of  these  insects,  since  they  facilitate  the  early 
deposition  of  the  eggs. 

Classification.  —  The  classification  of  insects  is  based  mainly 
on  three  characteristics:  the  type  of  development,  the  modifi- 
cation of  the  mouthparts,  and  the  number,  texture  and  venation 
of  the  wings.  All  blood-sucking  insects  have  mouthparts 
adapted  in  some  way  for  piercing  and  sucking,  but  the  types 
vary  greatly  in  different  groups.  Many  of  the  more  thor- 
oughly parasitic  insects,  e.g.,  lice,  bedbugs  and  "  sheep  ticks," 
have  secondarily  lost  their  wings  entirely,  or  have  them  in  a  rudi- 
mentary condition.  In  the  whole  order  of  Diptera  the  second 
pair  of  wings  is  reduced  to  inconspicuous  club-shaped  append- 
ages known  as  halteres. 

The  only  orders  of  insects  which  contain  species  of  interest  as 
human  parasites  are  the  Hemiptera  (Rhynchota),  or  true  bugs; 
the  Siphunculata,  or  sucking  lice;  the  Siphonaptera,  or  fieas;  and 
the  Diptera,  or  two-winged  flies.  These  four  orders  may  be 
briefly  summarized  as  follows: 

Hemiptera  (suborder  Heteroptera) :  metamorphosis  incom- 
plete; mouthparts  fitted  for  piercing  and  sucking,  the  piercing 
organs  being  ensheathed  in  the  jointed  lower  lip;  first  pair  of 
wings,  unless  reduced,  leathery  at  base  and  membranous  at  tip; 
second  pair  of  wings,  when  present,  membranous  with  relatively 
few  veins.     Human  parasites:   bedbugs,  cone-noses,  kissing  bugs. 

Siphunculata:  metamorphosis  incomplete;  mouthparts  fitted 
for  piercing  and  sucking,  and  retractile  into  a  pouch  under  pharynx; 
wings  secondarily  lost.     Human  parasites:  sucking  lice. 

Siphonaptera:  metamorphosis  complete;  mouthparts  fitted 
for  piercing  and  sucking,  the  piercing  organs  being  ensheathed 
in  the  labial  palpi,  and  the  mandibles  modified  as  protective 
flaps;  wings  secondarily  lost.     Human  parasites:  fleas,  chiggers. 

Diptera:  metamorphosis  complete;  mouthparts  fitted  for  pierc- 
ing and  sucking,  for  sucking  alone,  or  rudimentary;  first  pair 
of  wings  (absent  in  a  few  species)  membranous  with  few  veins; 
second  pair  of  wings  represented  only  by  a  pair  of  clubshaped 
organs,  the  halteres.  Human  parasites:  Sandflies,  mosquitoes, 
midges,  blackflies,  gadflies,  tsetse  flies,  stable-flies,  maggots  of 
various  species. 


CHAPTER  XX 
THE   MITES 

General  Account.  —  The  mites  and  ticks,  which  constitute  the 
Order  Acarina  of  the  Class  Arachnida,  are  only  slightly  known  by 
the  majority  of  people.  Popular  knowledge  of  them  is  usually 
limited  to  a  few  species  of  ticks,  chicken  mites,  and  perhaps  two 
or  three  other  species  of  mites.  Yet  the  group  includes  a  large 
number  of  species,  varying  in  size  from  some  ticks  which  are  half 
an  inch  or  more  in  length  to  mites  barely  visible  to  the  naked  eye. 
The  variety  of  body  form  is  great  and  some  species  when  magnified 
appear  ridiculously  grotesque.  The  majority  of  the  species  are 
more  or  less  round  or  oval,  with  head,  thorax  and  abdomen  all  in 
one  piece,  but  many  have  the  cephalothorax  (head  and  thorax 
fused  together)  distinctly  marked  off  from  the  abdomen,  while 
a  few  are  quite  wormlike  in  form.  Many  mites  are  free-living 
and  prey  upon  decaying  matter,  vegetation,  stored  foods  and 
the  like;  some  are  predaceous  and  feed  upon  smaller  animals; 
some  are  aquatic,  even  marine;  and  many  are  parasitic  on  other 
animals  during  all  or  part  of  their  life  cycle,  and  some  of  these 
serve  as  intermediate  hosts  for,  and  for  dissemination  of,  danger- 
ous disease  germs. 

Like  other  Arachnida  (spiders,  scorpions,  etc.)  the  mites  and 
ticks  usually  have  two  pairs  of  mouthparts  and  four  pairs  of 
legs,  though  the  last  pair  of  legs  is  not  acquired  until  after  the 
first  moult.  The  first  pair  of  mouthparts  or  chelicerae  are  some- 
times needle-like,  sometimes  shaped  like  a  grapnel  hook,  and 
very  often  pincer-like,  the  pincers  often  being  at  the  tip  of  a 
long  exsertile  needle-like  structure.  The  second  pair  of  mouth- 
parts, or  pedipalps,  are  simple  segmented  palpi.  In  many  kinds 
of  Acarina  the  anterior  end  of  the  ventral  side  of  the  body  is 
produced  as  a  sort  of  chin  or  lower  lip,  the  hypostome,  which 
may  be  needle-like  or  barbed  and  rasplike  (Fig.  152). 

The  digestive  tract  is  in  most  cases  well  developed.  Waves 
of  muscular  contraction  make  a  very  efficient  sucking  organ  of 

331 


332  THE   MITES 

the  pharynx.  The  stomach  has  pouches  opening  from  it  which 
act  as  food  reservoirs  (Fig.  149),  so  that  one  meal  may  last  for 
a  long  time.  The  intestine  is  usually  short  and  the  excretory 
organs,  malpighian  tubules,  open  into  it  not  far  from  the  anus. 
The  reproductive  organs,  as  in  other  Arachnida,  open  on  the  ventral 
surface  of  the  abdomen  but  at  different  places  in  different  species. 
The  nervous  system  is  largely  concentrated  into  a  great  mass, 
the  "  brain,"  lying  near  the  anterior  end  of  the  body  and  pierced 
by  the  oesophagus.  Many  mites  possess  tracheae,  similar  to 
those  of  spiders  and  insects,  for  breathing,  while  others,  soft- 
skinned  forms,  simply  absorb  oxygen  through  the  surface  of  the 
body. 

Life  History.  —  The  life  histories  of  mites  and  ticks  are  some- 
what variable,  but  usually  there  are  four  stages  in  their  develop- 
ment: the  egg,  the  larva,  the  nymph  and  the  adult  (see  Fig.  157). 
The  eggs  are  usually  laid  under  the  surface  of  the  soil  or  in  crev- 
ices, or,  in  some  parasites,  under  the  skin  of  the  host.  After  a 
varying  period  of  incubation,  which  depends  on  climatic  con- 
ditions, the  larva  hatches  in  the  form  of  a  six-legged  creature, 
often  quite  unUke  the  parent.  After  a  single  good  feed  of  blood 
or  plant  juices  the  larva  rests,  sheds  its  skin  and  appears  with 
an  additional  pair  of  legs  and  a  body  form  more  closely  resem- 
bling that  of  the  parent  but  without  developed  sexual  organs. 
The  nymph  thus  produced  feeds  again,  sheds  its  skin  from  one 
to  three  times  and  finally,  after  another  period  of  rest  during 
which  its  body  is  remodeled  for  the  second  time,  moults  again 
and  comes  forth  as  a  fully  adult  male  or  female,  ready  for  the 
reproduction  of  another  generation.  There  are  all  sorts  of  modi- 
fications of  this  order  of  development,  due  to  the  slurring  over  of 
one  phase  or  another.  One  of  the  most  aberrant  species  is  the 
louse-mite,  Pediculoides.  In  this  form  the  eggs  develop  within 
the  parent's  body  and  the  adult  males  and  females  issue  forth 
from  the  brood  chamber  improvised  for  them  out  of  the  abdomen 
of  the  mother  (Fig.  139). 

The  popular  opinion  that  all  mites  are  parasitic  is,  as  remarked 
before,  far  from  being  true.  Over  half  of  the  known  species  are 
not  parasitic  at  any  stage  in  their  life  history,  while  many  others 
are  parasites  only  during  part  of  their  life  cycle. 

Parasitism.  —  The  mites  are  an  interesting  group  for  the  study 
of  the  origin  of  parasitic  habits  since,  as  Ewing  has  shown,  para- 


HARVEST  MITES  333 

sitism  has  apparently  arisen  independently  in  different  families 
and  genera  at  least  eleven  times.  Nathan  Banks  in  his  treatise 
on  the  Acarina,  after  giving  a  number  of  interesting  examples  of 
peculiar  parasitic  habits,  writes  as  follows:  ''  We  can  only  explain 
these  remarkable  habitats  by  the  fact  that  mites,  especially  in 
their  immature  stages,  have  an  incontroUable  desire  to  go  some- 
where, and  get  into  every  cavity  and  crack  they  discover  in  their 
wanderings.  When  hungry  they  test  their  locality  for  food,  and 
if  not  too  different  from  their  previous  diet  this  new  habitat  may 
result  in  new  species  and  genera." 

A  few  species  of  mites  have  become  adapted  to  live  as  internal 
parasites,  but  all  the  species  normally  infesting  man  are  either 
external  or  subcutaneous  in  their  operations.  A  few  of  the 
species  which  are  not  averse  to  human  beings  as  food  are 
troublesome  and  irritating  enough  to  bring  their  whole  tribe  into 
disrepute.  The  families  of  mites  which  contain  species  annoying 
to  man  are  the  Ixodidce  and  Argasidce,  the  ticks;  Trombidiidce,  the 
harvest  mites  and  "  red-bugs  ";  Parasitidce  {Gamasidoe) ,  including 
the  chicken  mites;  Tarsonemidce,  including  the  louse-mite;  Ty- 
roglyphidce,  including  the  cheese  and  grain  mites;  Sarcoptidce,  the 
itch  mites;  and  Demodeddce,  the  hair-follicle  mites.  For  con- 
venience we  may  include  with  the  mites  the  very  aberrant  arach- 
nid forms  known  as  tongue-worms,  now  usually  placed  in  a 
distinct  order,  Linguatulina.  Since  the  ticks  are  popularly  looked 
upon  as  quite  distinct  from  other  Acarina,  and  form  a  very  im- 
portant group  of  the  order  on  account  of  their  role  as  disease 
carriers,  they  will  be  considered  in  a  separate  chapter. 

Harvest  Mites 

The  six-legged  larvae  of  the  harvest  mites,  family  Trombidiidae, 
known  as  red-bugs  or  chiggers,  are  very  annoying  pests,  and  one 
species,  the  Japanese  ''  akamushi  "  or  kedani  mite,  has  been 
proved  to  be  the  carrier  of  a  dangerous  disease,  kedani  or  flood 
fever.  Harvest  mites  are  little  scarlet-red  animals,  and  their 
larvae  are  tiny  pale-colored  creatures  barey  visible  to  the  naked 
eye  (Fig.  136).  According  to  one  writer  who  had  evidently 
experienced  them  a  red-bug  is  a  "  small  thing,  but  mighty;  a 
torturer  —  a  murderer  of  sleep;  the  tormentor  of  entomologists, 
botanists  and  others  who  encroach  on  its  domains;    not  that  it 


334 


THE  MITES 


bites  or  stings  —  it  does  neither;    worse    than  either,   it    just 
tickles." 

The  adult  harvest  mites  (Fig.  137)  are  law  abiding  members  of 
the  community,  and  attack  only  such  animals  as  plant-lice,  cater- 
pillars and  other  insects.  They  hibernate  in  soil  or  sheltered 
crevices  and  in  the  spring  lay  their  eggs,  several  hundred  apiece, 

in  the  ground  or  among  dead 
leaves.  The  eggs  are  very 
small,  round  and  brownish  in 
color,  and  were  once  classified 
O    as    fungous    growths!      The 


Fig.  136.  European  red-bug,  Leptus  au- 
tumnalis,  larva  of  a  Trombidium  usually 
thought  to  be  T.  holosericeum.  X  150. 
(After  Hirst.) 


Fig.  137.  An  adult  of  the 
kedani  mite,  a  Trombidiid. 
X  40.     (After  Nagayo  et  al.) 


newly  hatched  six-legged  larvae  creep  up  on  blades  of  grass 
or  plant  stems  and  await  an  opportunity  to  attach  them- 
selves to  an  insect.  If  successful  in  finding  a  host,  or  rather  in 
being  found  by  a  host,  the  mites  gorge  themselves  with  the 
juices  of  the  insect,  then  drop  to  the  ground,  crawl  to  some  snug 
hiding  place  and  undergo  a  transformation.  The  whole  inside 
of  the  body  is  remodeled,  a  fourth  pair  of  legs  is  acquired,  and 
after  a  few  weeks  the  skin  is  shed  and  an  adult  trombidiid  mite 
crawls  forth. 

It  is  while  the  larval  mites  are  hungrily  awaiting  the  arrival 
of  an  insect  upon  which  to  feed  that  they  attack  human  beings  or 
animals  which  may  pass  their  way.  They  are  so  small  that 
they  can  easily  pass  through  the  meshes  of  ordinary  clothing 
and  reach  the  skin,  where  they  set  up  a  severe  irritation  and 


ANNOYANCE  FROM   HARVEST  MITES  335 

intense  itching.  Some  authors  claim  that  the  mites  burrow  in 
the  skin  and  produce  inflamed  spots,  but  ordinarily  they  do  not 
go  beneath  the  skin  except  sometimes  to  explore  their  way  into 
the  long  tubes  of  the  sweat  glands.  The  habit  of  attacking 
warm-blooded  animals  is  evidently  abnormal,  (and  the  love  of 
blood  proves  ruinous  to  those  individuals  which  get  an  opportu- 
nity to  indulge  it,  since  they  soon  die  victims  of  their  own  per- 
verted appetites.     How  like  some  human  beingsIN 

The  irritation  caused  by  the  mites  is  probably  due  to  a  spe- 
cific poison  secreted  by  the  mites  rather  than  to  any  wounds  that 
they  make.  The  inflammation  of  the  skin  may  not  be  felt  for 
12  or  even  24  hours  after  infection  by  the  mites.  When  the  in- 
flammation does  commence  there  appear  large  red  blotches  on 
the  affected  parts  of  the  body  which  itch  intensely  and  are  made 
worse  by  scratching.  After  a  day  or  so  the  red  blotches  blister 
and  finally  scab  over.  Red-bug  rash  is  most  frequent  on  tender- 
skinned  people  and  on  those  parts  of  the  body  which  are  most 
exposed,  though  it  may  spread  over  the  whole  body  and  torment 
the  victim  unbearably.  Laborers  who  are  continually  exposed 
to  these  mites  seem  to  develop  an  immunity  to  the  mite  poison, 
and  suffer  little  or  none  from  them.  Herrick  states  that  one  of 
the  severest  infestations  he  ever  knew  was  contracted  by  a 
delicate-skinned  person  who  sat  down  on  the  ground  for  a  few 
minutes  on  some  golf  links  which  had  recently  been  laid  out  on 
an  old  pasture  where  there  was  still  much  long  grass.  This 
person's  body  became  covered  with  large  inflamed  spots  even  to 
the  neck.  The  torture  was  intense  for  a  week,  and  the  infection 
persisted  for  a  still  longer  period.  A  Mexican  species,  known  by 
the  Aztec  name  "  tlalsahuate,"  meaning  "  grain  of  earth,"  shows 
a  decided  preference  for  the  eyelids,  armpits,  groins  and  other 
thin-skinned  portions  of  the  body,  where  it  induces  itching  and 
inflammation,  and  even  ulceration  when  scratched.  The  "  b^te 
rouge  "  or  ''  Colorado  "  of  the  West  Indies  and  Central  America 
is  a  similar  if  not  identical  species. 

Sprinkling  sulphur  on  the  legs  and  inside  the  stockings  is  a 
necessary  preventive  measure  for  those  who  are  seriously  affected 
by  red-bugs,  and  who  have  to  walk  through  tall  grass  or  brush 
where  these  pests  abound.  A  hot  bath  shortly  after  infection, 
with  soap  or  with  soda  in  it,  gives  much  relief.  To  allay  the  itch- 
ing weak  ammonia  or  baking  soda  applied  to  the  affected  parts  is 


336  THE  MITES 

good,  and  alcohol,  camphor  and  other  cooUng  applications  are 
also  useful. 

Since  in  many  instances  the  adults  are  unknown,  the  larval 
harvest  mites  are,  for  the  sake  of  convenience,  placed  in  a  col- 
lective group,  Leptus,  and  the  name  is  used  in  the  manner  of  a 
generic  name.  The  common  red-bug  of  Europe,  for  instance, 
which  is  supposed  to  be  the  larva  of  Trombidium  holosericeum  is 
known  as  Leptus  autumnalis.  The  most  abundant  species  of 
red-bug  in  the  United  States  is  Leptus  irritans.  It  occurs  through- 
out the  southern  United  States  and  as  far  north  as  New  Jersey 
and  the  upper  Mississippi  Valley.  An  allied  species,  Leptus 
americanus,  also  occurs  in  many  parts  of  southern  United  States. 
On  the  northern  border  of  its  range  this  mite  does  not  appear 
until  the  latter  part  of  June  and  becomes  especially  annoying 
during  August,  but  its  season  becomes  earlier  and  earlier  the 
farther  south  it  occurs. 

The  European  harvest  mites,  the  commonest  of  which  is  Leptus 
autumnalis  (Fig.  136),  are  well  known  pests  throughout  Europe, 
especially  in  Central  and  Western  France,  where  they  are  known 
as  the  "  b^tes  rouges  "  or  "  rougets."  They  are  said  to  attack 
small  mammals,  such  as  rodents,  by  preference.  Unlike  the 
American  species,  the  European  harvest  mites  become  espe- 
cially abundant  in  the  fall  of  the  year.  Japanese  investigators 
have  recently  cast  doubt  on  the  commonly  accepted  belief  that 
Trombidium  holosericeum  is  the  parent  of  Leptus  autumnalis  since 
in  Japan  the  parent  of  the  kedani  mite  (Fig.  137),  which  very 
closely  resembles  L.  autumnalis^  is  quite  different  from  T.  holo- 
sericeum, whereas  an  adult  mite  which  very  closely  resembles 
the  latter,  produces  larvae  quite  different  from  L.  autumnalis. 

The  Japanese  harvest  mite,  larva  of  Trombidium  akamushi, 
known  locally  as  the  akamushi  (red-mite),  tsutsugamushi  (sick- 
ness mite)  and  kedanimushi  (hairy  mite),  has  been  proven  to  be 
the  carrier  of  a  typhus-like  disease  known  as  kedani  or  flood 
fever.  These  larval  mites  occur  in  countless  numbers  on  the 
local  field  mice,  Micromys  montebelloi,  living  especially  on  the 
inside  of  the  ear.  They  frequently  attack  the  farm  laborers 
who  engage  themselves  in  harvesting  and  handling  the  hemp 
which  is  raised  on  the  flood  plains  of  certain  Japanese  rivers.  It 
is  among  these  people  that  the  kedani  or  flood  fever  occurs, 
always  following  the  bite  of  a  mite.     The  bite,  usually  in  the 


LOUSE-MITE 


337 


armpits  or  on  the  genitals,  is  at  first  painless  and  unnoticed, 
but  the  mite  remains  attached  at  the  wound  from  one  to  three 
days  before  dropping  to  the  ground  to  transform  to  the  nymphal 
stage.  The  bite  of  the  mite  is  said  to  develop  into  a  tiny  sore  or 
inflamed  spot  in  the  region  of  which  the  lymph  glands  become 
swollen  and  painful  and  flood  fever  follows.  The  nymphs  and 
adults  of  this  mite  have  recently  been  found  by  Nagayo  and  his 
fellow-workers  in  Japan. 

The  transmission  of  kedani  by  this  mite  is  the  only  positive 
instance  of  human  disease  carried  by  Acarina  other  than  ticks. 


Other  Occasionally  Parasitic  Species 

There  are  many  species  of  mites,  of  several  different  families, 
which  under  abnormal  circumstances  or  by  sheer  accident  may 
become  troublesome  parasites  of  man.     Nearly  all  mites  secrete 
salivary  juices   which   have 
a  toxic  effect  when  injected 
into    the    blood;    therefore 
any    mite    which    will    bite 
man     under     any     circum- 
stances may  become  a  pest. 
In  nearly  all  cases  the  symp- 
toms of  attacks  by  mites  are 
similar — hivelike  or  rashlike 
eruptions    of   the    skin,    in- 
tense itching  and  in  severe 
attacks  fever. 

Louse-Mite 
most  important  of  the  occa- 
sionally parasitic  mites  is 
the  louse-mite,  Pediculoides  ventricosus  (Fig.  138),  belonging 
to  the  family  Tarsonemidse.  This  is  a  very  minute  species, 
barely  visible  to  the  naked  eye,  which  is  normally  parasitic 
on  grain-moth  caterpillars  and  other  noxious  insects,  and  there- 
fore beneficial.  These  mites  live  in  stubble,  stored  grain  and 
beans,  cotton  seeds,  straw,  etc.,  attacking  the  various  insects 
which  infest  these  products  and  becoming  numerous  in  pro- 
portion to  the  abundance  of  their  prey.  The  female  has  the 
remarkable  habit  of  retaining  the  eggs  and  young  in  her  abdomen 


Fig.  138.     Louse-mite,  Pediculoides  ventri- 
One  of  the     cosus;    9.  unimpregnated  female;    $,  male, 
X  150.      ( 9 .   after  Brucker  from  Webster; 
$ ,  after  Banks.) 


338 


THE  MITES 


until  they  have  become  fully  developed  males  and  females.  Her 
abdomen  in  consequence  becomes  enormously  distended  so  that 
the  rest  of  the  body  appears  as  only  a  tiny  appendage  at  one  side 
of  it.  A  gravid  female  (Fig,  139)  fully  distended  may  reach  a 
diameter  of  1.5  mm.  (^V  of  an  inch)  whereas  normally  she  measures 
only  0.2  mm.  {j^s  of  an  inch)  in  length.  Under  the  most  favorable 
conditions  only  six  days  may  elapse  from  the  time  the  young 
females  emerge  from  the  mother  before  they  reproduce  a  brood  of 

their  own.  The  brood  varies 
in  number  from  a  few  dozen 
to  over  200. 

Like  many  other  beneficial 
things,  these  predaceous  little 
mites  may  become  a  distinct 
nuisance,  and  many  serious 
outbreaks  of  infestation  of 
human  beings  by  them  are  on 
record,  especially  among  the 
grain  threshers  of  the  central 
portion  of  the  United  States 
and  among  laborers  who  handle 
stored  grains  and  other  dry 
foods.  In  our  Middle  West 
their  attacks  have  often  been 
^^«^  attributed  to  harvest  mites.  In 
Italy  the  rash  produced  by 
louse-mites  is  called  "  miller's  itch."  Several  outbreaks  have 
occurred  in  the  United  States  due  to  the  use  of  new  straw  mat- 
tresses. The  transformation  of  all  the  grain-moth  caterpillars 
into  moths  leaves  the  mites  with  their  normal  food  supply  cut 
off,  and  they  are  then  ready  to  feed  upon  any  flesh  to  which  they 
may  have  access  in  an  effort  to  prevent  starving  to  death. 

The  itching  rash  produced  begins  about  12  to  16  hours  after 
exposure  to  the  mites.  At  first  they  produce  pale  hivelike  spots, 
which  later  become  red  and  inflamed,  and  itch  unbearably. 
Little  blisters,  the  size  of  a  pinhead  or  larger,  appear  at  the  sites 
of  the  bites  and  these  later  develop  into  httle  pustules.  Scratch- 
ing results  in  the  formation  of  scabs,  and  when  these  fall  off 
dark  spots  which  are  slow  to  fade  are  left  on  the  skin.  The 
rash  and  itching  normally  disappear  within  a  week  unless  fresh 


Fig.   139.     Louse-mite,  gravid  female 
X    about     75.     (After     Brucker 
Webster.) 


GRAIN  MITES  339 

detachments  of  mites  are  constantly  acquired.  In  severe  in- 
festations the  irritation  and  poisoning  is  sufficient  to  cause 
constitutional  symptoms  such  as  fever,  high  pulse,  headache, 
nausea,  etc. 

Since  the  mites  cannot  thrive  on  human  blood,  and  remain 
attached  to  the  skin  for  only  a  short  time,  no  treatment  for 
destroying  them  is  necessary.  Remedies  to  relieve  the  itching, 
such  as  the  application  of  soda  or  soothing  ointments,  or  warm 
baths  with  a  little  soda,  are  called  for.  To  prevent  infection 
when  handling  infected  produce,  Dr.  Goldberger,  of  the  United 
States  Public  Health  Service,  suggested  a  greasing  of  the  body, 
followed  by  a  change  of  clothes  and  a  bath  after  working  with 
the  infected  material.  Riley  and  Johannsen  suggest  the  use  of 
powdered  sulphur  as  a  preventive  in  view  of  its  efficiency  against 
harvest  mites.  Control  of  the  mite  consists  largely  in  keeping 
grain  and  other  dry  produce  as  free  as  possible  from  the  insects 
on  which  the  mites  feed.  Burning  stubble  in  winter  and  threshing 
wheat  directly  from  the  shock  would  tend  to  lessen  the  worms  in 
stored  wheat  and  with  them  the  mites. 

Grain  Mites.  —  The  family  Tyroglyphidse,  including  many 
species  of  mites  which  normally  feed  on  grain,  flour,  sugar,  dried 
fruits,  cheese  and  other  foods,  contains 
several  species  which  become  annoying  to 
man  and  produce  an  itching  rash  on  people 
who  handle  infested  goods. 

According  to  Banks  all  the  members  of 
this  family  are  pale-colored,  soft-bodied 
mites,  with  prominent  pincer-like  chelicerse 
and  no  eyes.  Their  bodies  are  about 
twice  as  long  as  wide  and  are  furnished 
with  a  few  scattered  long  hairs  (Fig.  140). 

The  life  history  of  some  members  of  the  Tymgiylhus  lonj^^  x  3o! 
family  is  quite  remarkable  in  that  there  is  (After  Fumouze  and 
added  a  phase  of  existence  which  does  not 

occur  in  other  mites.  All  the  species  scatter  their  eggs  haphazard 
over  the  infected  material.  Upon  hatching  the  larvae  have  six 
legs  and  acquire  a  fourth  pair  after  moulting,  in  orthodox  mite 
style.  Some  now  develop  directly  into  adults,  while  others  go 
through  what  is  called  a  "  hypopus  "  stage.  The  hypopus  (Fig. 
141)  is  very  different  from  the  nymph  from  which  it  develops; 


340  THE  MITES 

the  body  is  hard  and  chitinous,  there  is  no  mouth  or  mouthparts, 
the  legs  are  short  and  stumpy,  and  there  is  usually  a  raised  area 
on  the  ventral  surface  with  a  number  of  tiny  sucking  discs.  By 
means  of  these  suckers  the  hypopus  attaches  itself  to  insects  or 
other  creatures  and  is  thus  transported  to 
new  localities,  the  entire  object  of  the 
hypopus  stage  apparently  being  to  secure 
passage  to  new  breeding  grounds.  After 
dropping  from  its  unwilling  transporter 
the  hypopus  moults  into  an  eight-legged 
nymph  again,  which,  after  feeding,  develops 
into  an  adult. 

The  Tyroglyphidse  are  all  quite  similar 
Fig.  141.    Hypopus  or  -j^  appearance,  and  the  characters   which 

traveling   stage    of    Tyro-  ,  ,  , 

glyphus,    ventral    view.   Separate  the  species,  and  even  the  genera, 
Much  enlarged.      (After  ^j.^  f^^  ^^d  minute.     A  considerable  num- 

Banks.)  »  . 

ber  of  species  may  attack  persons  who 
handle  infested  materials,  and  they  are  the  cause  of  "  grocers' 
itch."  This  affliction  is  caused  especially  by  various  species 
of  Glyciphagus  and  Tyroglyphus.  Of  historical  interest  is  a 
case  of  dysentery  apparently  due  to  a  Tyroglyphus,  T.  longior, 
(Fig.  140)  which  occurred  in  one  of  Linnaeus'  students.  The 
mites  were  abundant  in  his  faeces,  and  were  found  to  live  and 
multiply  in  a  juniper-wood  cup  which  he  used.  As  shown  by 
Castellani,  an  itching  rash  known  as  ''  copra  itch,"  occurring 
among  the  laborers  in  the  copra  mills  of  Ceylon  where  cocoanut 
is  ground  up  for  export,  is  caused  by  a  variety  of  this  mite,  called 
T.  longior  castellanii.  Copra  itch  occurs  also  among  stevedores 
who  handle  copra  in  London.  Another  species,  Glyciphagus 
huski,  was  taken  from  beneath  the  skin  on  the  sole  of  the  foot 
of  a  negro  in  England;  it  had  caused  large  sores.  The  negro 
attributed  the  affliction  to  the  wearing  of  a  pair  of  shoes  loaned 
him  by  a  similarly  affected  negro  from  Sierra  Leone,  Africa. 
Another  species,  Rhizoglyphus  parasiticus,  which  lives  on  roots, 
bulbs,  etc.,  in  India,  produces  a  skin  disease  among  coolies  work- 
ing on  tea  plantations.  It  begins  with  blisters  between  the  toes 
and  spreads  to  the  ankles,  causing  very  sore  feet. 

Other  Species.  —  A  few  species  of  the  family  Tetranychidse, 
including  the  ''  red  spiders "  or  spinning  mites,  occasionally 
become  troublesome  to  man,  although  they  are  normally  vege- 


SPECIES    OCCASIONALLY    ANNOYING 


341 


table  feeders  and  may  do  much  damage  to  cultivated  plants. 
One  species  especially,  Tetranychus  molestissimus,  which  lives 
on  the  undersides  of  leaves  of  a  species  of  cockle  bur,  Xanthium 
macrocarpum,  in  Argentina  and  Uruguay,  attacks  man  during 
the  winter  months  from  December  to  February.  It  produces 
symptoms  similar  to  those  of  the  louse-mite,  with  intense  itching 
and  some  fever.  The  common  "  red  spider,"  T.  telarius,  an 
almost  cosmopolitan  species,  also  is  reported  to  attack  man  oc- 
casionally. 

The  common  chicken  mite,  Dermanyssus  gallinae,  belonging 
to  the  family  Parasitidae  (Gamasidse),  frequently  causes  much 
irritation  and  annoyance  to  those  who  come  in  contact  with  it. 
Although  it  can  thrive  and  multiply  only  on  certain  kinds  of 
birds,  it  sometimes  remains  on  mammals  for  some  time,  causing 
an  eczema  or  rashlike  breaking-out  on  the  skin,  attended,  as  in 
other  mite  infections,  by  intense  itching.  Except  in  cases  of 
constant  reinfection  chicken  mites  are  usually  troublesome  to 
man  for  only  a  few  days  at  most.  Since  these  mites  can  live 
for  several  weeks  without  feeding  on  their  normal  hosts,  places 
formerly  frequented  by  fowls  may  be  infective  after  the  removal 
of  the  birds.  The  mites  norm.ally  remain  on  their  hosts  only  long 
enough  to  fill  up  on  blood,  usually  at  night,  spending  the  rest  of 
the  time  in  cracks  and  crevices  in  and  about  the  coops.  Various 
sprays  of  sulphur,  carbolic  solutions  and  oils  are  used  to  destroy 
them.  An  allied  species,  Holothyrus  coccinella,  living  on  geese  and 
other  birds  on  Mauritius  Island,  attacks  man,  causing  burning  and 
swelling  of  the  skin,  and  frequently  proves  quite  dangerous  to 
children  by  entering  the  mouth. 

A  very  small  mite,  Tydeus  molestus,  belonging  to  the  family 
Eupodidae,  attacks  man  in  much  the  same  manner  as  do  the 
harvest  mites.  It  is  common  on  some  estates  in  Belgium,  ap- 
parently having  been  imported  many  years  ago  with  some  Peru- 
vian guano.  It  appears  regularly  each  summer  on  grass  plots, 
bushes,  etc.,  in  great  numbers,  disappearing  again  with  the  first 
frost.  It  causes  great  annoyance  in  red-bug  fashion,  not  only  to 
man  but  to  other  mammals  and  birds  as  well. 


342 


THE  MITES 


Itch  Mites 

The  itch  mites,  belonging  to  the  family  Sarcoptidae,  are  the 
cause  of  scabies  or  mange  in  various  kinds  of  domestic  and  wild 
animals,  and  of  "  itch  "  in  man.  This  disease  is  one  which  has 
been  known  for  a  very  long  time  but  was  formerly  supposed  to  be 
caused  by  "  bad  blood  "  or  other  constitutional  disorders  such 
as  cause  the  growth  of  pimples.  Even  at  the  present  time  the 
true  cause  of  the  disease  is  not  understood  by  the  majority  of 
people. 

The  Parasites.  —  The  itch  mites  (Fig.  142)  are  minute  whitish 
creatures,  scarcely  visible  to  the  naked  eye,  of  which  the  females 


Fig.  142. 


Human  itch  mite,  Sarcoptes  scabiei;  9 »  female ;   $ 
100.     (Partly  after  Banks.) 


male.      X  about 


burrow  beneath  the  skin  and  lay  eggs  in  the  galleries  which  they 
make.  They  are  nearly  round  and  the  cuticle  is  delicately 
sculptured  with  numerous  wavy  parallel  lines,  pierced  here  and 
there  by  stiff  projecting  bristles  or  hairs.  There  are  no  eyes 
or  tracheae.  The  cone-shaped  mouthparts  are  covered  over  by 
the  shieldlike  upper  lip.  The  legs  are  short  and  stumpy  and  are 
provided  with  sucker-like  organs,  called  ambulacra,  at  their 
tips.  In  the  female  the  two  posterior  pairs  of  legs  terminate 
in  a  simple  long  bristle,  whereas  in  the  male  only  the  third  pair 
of  legs  terminates  in  bristles.  The  human  itch  mite,  Sarcoptes 
scabiei,  is  only  slightly  distinguishable  from  the  itch  mites  which 
cause  scabies  and  mange  in  many  of  our  domesticated  animals. 
Each  infected  species  of  mammal  has  its  own  variety  of  itch 


ITCH    MITES  — LIFE    HISTORY 


343 


mite,  but  many  of  them  can  be  transferred  readily  from  one 
host  to  another.  In  the  common  human  species  the  male  is 
only  about  0.25  mm.  (y^^  of  an  inch)  in  length,  while  the  female  is 
about  0.4  mm.  (^V  oi  an  inch)  in  length.  A  variety  of  this  mite, 
S.  scahiei  crustosce,  causing  the  so-called  ''  Norwegian  itch,"  is 
found  in  northern  Europe  and  occasionally  in  the  United  States, 
but  is  always  rare.  The  disease  caused  by  it  differs  in  some  re- 
spects from  ordinary  itch.  Still  another  species,  Notoedres  cati, 
which  causes  a  very  persistent  and  often  fatal  disease  in  cats, 
temporarily  infests  man,  but  is  apparently  unable  to  breed  in 
human  skin,  since  the  infection  dies  out  in  a  week  or  two. 

The  impregnated  females  of  itch  mites  excavate  tortuous  tun- 
nels in  the  epidermis  (Fig.  143)  especially  on  such  portions  as 


Fig.  143.     Diagrammatic  tunnel  of  itch  mite  in  human  skin,  showing  female 
depositing  eggs.      X  about  30.     (Adapted  from  Riley  and  Johannsen.) 

between  the  fingers  and  toes,  on  the  groins  and  external  genitals, 
and  in  the  armpits,  where  the  skin  is  delicate  and  thin.  The 
tunnels  are  anywhere  from  a  few  millimeters  to  over  an  inch  in 
length,  and  are  usually  gray  in  color  from  the  eggs  and  excrement 
deposited  by  the  female  as  she  burrows.  The  daily  excavations 
of  a  mite  amount  to  two  or  three  millimeters. 

The  eggs  (Fig.  143)  vary  in  number  from  15  to  50.  They  are 
laid  in  groups  of  from  two  to  four,  the  mite  resting  after  each 
oviposit  ion.  After  they  are  all  laid  the  female  dies,  usually  at 
the  end  of  a  single  tortuous  burrow.  The  eggs  hatch  in  from  three 
to  six  days  into  six-legged  larvae.  The  latter  transform  in  two  or 
three  days  into  nymphs.  The  nymphs  commonly  build  burrows 
for  themselves  and  moult  twice,  the  second  time  becoming  adult 


344  THE   MITES 

male  and  female  mites.  .  -l^he  duration  of  the  two  nymphal  periods 
is  from  three  and  one-half  to  six  days,  the  entire  development  of 
the  mites  therefore  requiring  from'  nine  to  sixteen  days.  The 
mites  are  not  necessarily  nocturnal  as  was  formerly  supposed, 
but  wander  about  on  the  surface  of  th^  skin  when  the  latter  is 
warm,  which  is  most  frequently  tht&  ease  when  the  host  is  in  bed. 
Copulation  takes  place  on  the  surface  of  the  skin,  and  apparently 
the  males  do  not  burrow  or  enter  the  burrows  made  by  the  fe- 
males, but  merely  hide  under  superficial  dead  cells  of  the 
epidermis.  Since  they  die  very  soon  after  copulation,  they  are 
seldom  found.  The  young  impregnated  females  soon  begin 
fresh  excavations,  and  produce  more  eggs.  Fifteen  or  twenty 
eggs  each  generation,  of  which  approximately  two-thirds  are 
females,  and  a  new  generation  about  every  four  weeks,  results 
in  an  enormous  rate  of  increase.  In  less  than  six  months  the 
progeny  of  one  pair  of  itch  mites  theoretically  would  number 
several  millions! 

The  Disease.  The  "  itch  "  is  a  disease  which  in  the  past  has 
swept  over  armies  and  populations  in  great  epidemics,  but  it  has 
decreased  with  civilization  and  cleanliness,  and  is  fortunately 
less  common  now,  at  least  in  civilized  communities. 

As  its  name  implies,  the  disease  is  characterized  by  itching  of 
the  most  intense  kind  where  the  mites  burrow  in  the  skin.  The 
itching  is  probably  due  only  to  a  very  slight  extent  to  the  me- 
chanical irritation  in  the  skin,  but  is  induced  rather  ]3y  poisonous 
substances  secreted  or  excreted  by  the  mites.  Injection  of  fluid 
containing  crushed  mites  produces  an  eruption  and  irritation 
similar  to  that  caused  by  the  burrowing  of  the  living  mites. 

The  excretions  of  the  mites  as  they  feed  in  their  burrows  form 
little  hard  pimples,  about  the  size  of  a  pinhead  or  a  little  larger, 
containing  yellow  fluid.  When  these  are  scratched,  as  they  are 
almost  certain  to  be  on  account  of  the  unbearable  itching,  they 
frequently  become  secondarily  infected  and  may  give  rise  to 
larger  sores.     Ultimately  scabs  form  over  them. 

Since  the  entire  life  history  of  the  parasites  is  passed  on  a 
single  host,  generation  after  generation  may  develop  from  a 
single  infection,  and  although  the  infection  apparently  may  dis- 
appear temporarily,  it  persists  recurrently  for  many  years.  Since 
the  mites  are  sensitive  to  cold  the  infected  areas  of  skin  not  only 
do  not  spread  but  may  become  restricted  during  the  winter,  to 


ITCH  345 

spread  with  renewed  vigor  with  the  corning  of  warm  weather. 
So  persistent  is  the  infection  that  it  is  doubtful  whether  it  ever 
spontaneously  dies  out.  "  Norwegian  itch,"  caused  by  Sar copies 
scahiei  crustosce,  is  even  more  persistent,  and,  unlike  ordinary  itch, 
may  occur  on  the  face  aiid  scalp  as  well  as  on  other  parts  of  the 
body.     Gigantic  crusts  form  b^r  the  infected  parts. 

Infection  can  result  only  from  the  passage  of  male  and  female 
mites,  or  of  an  impregnated  female,  from  an  infected  to  a  healthy 
individual.  Normally  this  takes  place  by  actual  contact,  rarely 
in  the  daytime  on  account  of  the  secretive  habits  of  the  mites, 
but  commonly  at  night,  especially  from  one  bedfellow  to  another. 
Gerlach  experimented  to  determine  how  long  the  mites  could 
live  away  from  their  hosts  and  found  that  in  the  dry  warm  air  of 
a  room  they  lost  vitality  so  rapidly  that  they  could  not  be  re- 
vived after  three  or  four  days.  In  moist  places,  on  the  other 
hand,  such  as  in  the  folds  of  soiled  underwear  or  bedcloths,  they 
survived  as  long  as  ten  days.  From  this  it  is  evident  that  in- 
fection may  take  place  by  means  of  bedding,  towels,  underwear 
or  other  cloth  which  may  come  in  contact  with  infected  skin. 
The  author  once  witnessed  an  epidemic  of  itch  arising  from  the 
use  of  an  infected  wrestling  mat  in  a  college  gymnasium.  (  It  is 
also  possible  for  infection  to  be  derived  from  mangy  animals, 
though  the  mites,  once  adapted  for  several  generations  to  a 
given  host,  do  not  survive  a  transfer  to  a  different  species  of  host 
more  than  a  few  days.^ 

Treatment  and  Prevention.  —  The  treatment  of  itch  before 
the  nature  of  the  malady  was  understood  was  considered  very 
slow  and  difficult,  and  even  at  the  present  time  it  is  looked  upon 
by  many  people  as  a  disease  which  can  be  recovered  from  only 
after  prolonged  treatment.  The  fact  that  the  mites  burrow 
beneath  the  skin  to  lay  their  eggs  makes  careless  superficial 
treatment  almost  as  inefficient  as  the  internal  medicine  which 
was  once  taken  to  "  purify  the  blood."  The  most  effective 
treatment  for  the  itch  is  as  follows:  the  patient  rubs  himself 
vigorously  with  green  soap  and  warm  water  for  about  20  minutes, 
and  follows  this  with  a  warm  bath  for  half  an  hour  or  more,  dur- 
ing which  the  soapy  massage  continues.  In  this  manner  the 
skin  is  softened,  the  pores  opened  and  the  burrows  of  the  mites 
soaked  so  that  the  application  of  mite  poison  which  is  to  follow 
will  penetrate  more  readily.     When  the  skin  is  thus  prepared 


346  THE   MITES 

some  substance  for  destroying  the  mites  is  applied.  Sulphur 
ointment  made  by  mixing  one-half  an  ounce  of  sulphur  to  ten 
ounces  of  lard,  is  excellent;  its  virtue  lies  in  the  formation  of 
hydrogen  sulphide  in  contact  with  the  skin,  sulphur  itself  being 
inert.  A  still  more  efficient  though  more  expensive  remedy  is 
•a  beta-naphthol  ointment,  prepared  as  follows:  beta-naphthol, 
75  grains;  olive  oil,  2 J  fluid  grams;  sulphur,  1  oz.;  lanolin,  1  oz.; 
green  soap,  1  oz.  One  of  these  applications,  or  some  other,  is 
unsparingly  rubbed  into  the  skin  of  the  infected  portions  of  the 
body,  and  of  a  considerable  area  around  them.  When  rubbed 
in  for  20  or  30  minutes  the  patient  goes  to  bed,  leaving  the  oint- 
ment on  his  body  until  morning  when  it  is  washed  off  with  another 
bath.  Meanwhile  the  soiled  underwear,  bedclothes  or  other 
possibly  infected  articles  are  sterilized  by  boiling  or  baking. 
Since  this  course  of  treatment  does  not  destroy  the  eggs  it  is 
repeated  in  about  ten  days  in  order  to  destroy  any  mites  which 
may  have  hatched  in  the  meantime. 

For  delicate-skinned  individuals  the  treatment  described  above 
is  too  severe  and  may,  of  itself,  give  rise  to  inflammation  of  the 
skin  not  unlike  that  caused  by  the  mites.  In  such  case  balsam 
of  Peru  may  be  used  satisfactorily  instead  of  sulphur  ointment, 
but  should  be  rubbed  in  several  times  at  intervals  of  a  few  hours. 
It  does  not  cause  any  irritation. 

Prevention  of  this  annoying  infection  consists  merely  in  avoid- 
ing contact  with  infected  individuals,  and  of  shunning  public 
towels  or  "soiled  bed  linen.  A  single  infected  individual  in  a 
logging  or  railroad  camp  may  be  a  means  of  infecting  the  entire 
camp.  Means  should,  therefore,  be  taken  to  guard  against 
such  individuals  whenever  possible,  and  to  prevent  the  spread 
of  infection  from  unsuspected  individuals  by  care  as  regards  the 
use  of  towels  and  bed  clothes. 

Hair  Follicle  Mites 

The  hair  follicle  or  face  mite,  Demodex  folliculorum  (Fig.  144), 
of  the  family  Demodecidse,  is  a  species  which  is  most  strikingly 
adapted  for  its  parasitic  life.  It  is  a  wormlike  creature,  very 
unmite-like  in  general  appearance,  which  lives  in  the  hair  follicles 
and  sebaceous  glands  of  various  mammals.  In  man  it  occurs 
especially  on  the  face. 


HAIR-FOLLICLE    MITE 


347 


The  wormlike  appearance  of  the  adult  mites  is  due  to  the  great 
elongation  of  the  abdomen  which  is  marked  by  numerous  fine 
lines  running  around  it.  The  beak  is  short  and  broad,  and  the  four 
pairs  of  legs,  all  similar,  are  short,  stumpy,  three-jointed  append- 
ages. The  female  mites  are  .35  to  .40  mm. 
long  (about  ^  of  an  inch),  while  the  males  are 
a  little  smaller. 

The  multiplication  of  these  mites  is  slow. 
The  eggs  hatch  into  tiny  six-legged  larvae  in 
which  the  legs  are  mere  tubercles.  It  requires 
four  moults  to  bring  the  larvae  to  sexual 
maturity. 

In  most  cases  these  parasites  cause  no  incon- 
venience whatever  and  their  presence  is  not 
even  suspected.  In  Europe  a  large  proportion 
of  people  are  said  to  be  infected,  but  in  Amer- 
ica, according  to  Riley  and  Johannsen,  there  is 
reason  for  believing  that  the  infection  is  far 
less  common  than  is  usually  supposed.  Since 
"generation  after  generation  may  be  produced 
on  a  single  host  the  infection  is  potentially 
indefinite  in  its  duration.  When  the  mites 
become  numerous  in  the  hair  follicles 
sebaceous  glands  they  sometimes  cause  "  black 
heads  "  by  causing  a  fatty  accumulation  to  be  produced,  but 
they  are  not  the  only  or  even  the  usual  cause  of  "black-heads.'' 
The  skin  disease  known  as  ''  acne  "  has  also  been  attributed  to 
these  mites,  but  probably  erroneously.  Follicle  mites  have  been 
suspected  also  of  spreading  leprosy. 

The  method  of  transmission  of  the  mites  to  another  host  is 
not  definitely  known  but  it  is  probable  that  the  adults  wander 
on  the  surface  of  the  skin  at  times,  and  may  then  be  transmitted 
by  direct  contact  or  by  towels,  as  are  itch  mites.  In  dogs, 
where  the  follicle  mite,  possibly  a  different  species,  causes  a  very 
severe  and  often  fatal  form  of  mange,  transmission  from  dog 
to  dog  takes  place  in  a  very  irregular  manner,  and  there  are 
frequent  instances  cited  of  infected  dogs  associating  for  a  long 
time  with  uninfected  ones  without  spreading  the  disease.  Ex- 
periments with  transmission  of  the  canine  follicle  mite  to  man 
have  invariably   failed.     Little   is   known   about   treatment   of 


Fig.    144.      Hair- 
follicle  mite,   Demo- 
dex   folliculorum.     X 
or    200.       (After    Meg- 
nin.) 


348  THE  MITES 

Demodex  infection,  but  it  is  probable  that  sulphur  applications 
in  some  form  would  reach  and  destroy  them. 

Tongue-worms 

Related  to  the  mites,  but  now  placed  in  a  distinct  order,  Lin- 
guatulina,  are  the  tongue- worms.  These  animals  have  become  so 
modified  by  parasitic  life  that  the  adults  have  lost  nearly  all  re- 
semblance to  the  other  members  of  their  group,  and  have  become 
so  wormlike,  both  in  form  and  life  history,  as 
to  have  been  classified  by  older  writers  with 
the  tapeworms  (Fig.  146A).  Only  the  larval 
stage  gives  a  clue  to  their  real  relationships. 
Their  long  bodies  are  either  flattened  or 
cylindrical,  and  distinctly  divided  into  rings 
or  segments  as  in  leeches.  There  is  no  dis- 
tinct demarcation  between  head,  thorax  and 
abdomen.  On  either  side  of  the  mouth  are 
of^Porocephaius  a^mif-  ^^o  hooks  which  can  be  retracted  into  grooves 
latus.  X  3.  (After  like  the  claws  of  a  cat  (Fig.  145) .  These  are 
^^  usually  looked  upon  as  the  vestiges  of  some  of 

the  appendages.  At  the  bases  of  the  retractile  hooks  there  open 
a  number  of  large  glands,  the  secretion  of  which  is  believed  to  have 
blood-destroying  power.  The  internal  organization  of  the  body 
is  degenerate  in  the  extreme;  there  is  no  blood,  no  respiratory 
system,  no  special  sense  organs,  no  organs  of  locomotion;  little 
more  than  the  barest  necessities  of  racial  existence  —  a  simple 
nervous  system,  a  digestive  tract  and  a  reproductive  system. 
The  sexes  are  separate. 

The  adult  worms  live  in  the  nostrils,  trachse  or  lungs  of  car- 
nivorous reptiles  and  mammals,  where  they  produce  their  myriads 
of  eggs.  The  latter  are  voided  with  the  catarrhal  products  of 
the  respiratory  system  caused  by  the  presence  of  the  parasites. 
The  egg-laden  mucous  excretions  from  the  nose  of  an  infected 
animal  are  dropped  on  vegetation  and  eaten  by  herbivorous  ani- 
mals, whereupon  the  eggs  (Fig.  146B)  develop  into  larvae  in  the 
new  host.  These  larvae  (Fig.  146C),  hatched  out  in  the  stomach, 
are  far  more  mitelike  than  the  adults,  inasmuch  as  they  possess 
two  pairs  of  rudimentary  legs  and  primitive  arthropod  mouth- 
parts.      The  larvae  migrate  to  the  liver,  spleen  or  other  organs 


LINGUATULA    RHINARIA 


a49 


and  there  encyst  (Fig.  146D).  After  a  series  of  moults  a  second 
larval  stage  is  entered  upon,  this  time  with  a  wormlike  appear- 
ance much  more  like  that  of  the  adult  (Fig.  146E). 

At  this  stage  a  "  wanderlust  "  seizes  the  tongue- worm  and  it 
begins  an  active  migration  in  an  endeavor  to  reach  a  more  satis- 
factory site  for  adult  life.     The  mites  may  settle  in  the  res- 


BCKUS) 


Fig.  146.  Life  history  of  tongue- worm,  Linguatula  rhinaria;  A,  adult  female 
from  nasal  passage  of  dog;  B,  egg  containing  embryo;  C,  larva  from  sheep,  man  or 
other  animals;  D,  encysted  larva;   E,  2nd  larval  stage,  from  liver  of  sheep  or  man. 

piratory  tract  of  their  original  host,  or  may  abandon  their  host 
by  way  of  throat  or  anus  to  take  chances  on  being  snuffed  up  or 
taken  into  the  mouth  cavity  of  another  animal.  Having  gained 
access  to  their  final  habitat  in  the  nostrils  or  lungs,  they  attach 
themselves  by  their  hooks,  moult,  copulate  and  reproduce. 

While  both  larval  and  adult  stages  of  tongue-worms  are  oc- 
casionally found  in  man,  the  larvae,  as  liver  parasites,  are  more 
common. 

The  tongue-worm  most  frequently  observed  in  man  is  Lingua- 
tula rhinaria.  The  male  of  this  species  is  a  small  worm,  whitish 
in  color,  about  three-fourths  of  an  inch  in  length,  whereas  the 
female  (Fig.  146 A),  which  is  yellowish  or  brownish  due  to  the 
eggs  in  her  body,  reaches  a  length  of  from  three  to  five  inches. 
The  adults  occur  most  commonly  in  the  nasal  passages  of  dogs 
(Fig.  147).  The  eggs  (Fig.  146B)  are  dispersed  with  mucus 
during  the  violent  fits  of  sneezing  to  which  the  presence  of  the 
parasite  gives  rise.  The  swallowing  of  food  or  drink,  especially 
grass  or  vegetables,  soiled  by  this  infective  mucus,  results  in  the 
access  of  the  larva-containing  eggs  to  the  intermediate  host,  which 
is  most  frequently  sheep,  goats,  rabbits,  etc.,  but  occasionally 


350 


THE  MITES 


man.  In  the  course  of  five  or  six  months  the  larvae  (Fig.  146C), 
having  migrated  to  the  Hver  or  lymph  glands,  transform  to  the 
second  larval  stage  (Fig.  146E),  reach  a  length  of  about  one- 


FiQ.   147.     Head  of  a  dog  split  in  half  to  show  three  tongue-worms,  Linguatula 
rhinaria,  (a)  in  the  nasal  cavity.     Reduced  in  size.     (After  Colin,  from  Hall.) 


fourth  of  an  inch,  and  consist  of  from  80  to  90  rings  or  segments, 
each  one  with  very  fine  denticulations  on  the  hind  margin.     For 

a  long   time   this   larva   was   looked 
upon  as  a  distinct  species.     L.  rhinaria 


is    nowhere    abundant,    even    in    its 


normal  hosts,  though  in  some  parts  of 
Europe  about  ten  per  cent  of  dogs  are 
said  to  be  infected.  The  majority 
of  human  cases  reported  have  been 
in  Germany. 

Another  species  which  is  occasion- 
ally found  as  a  parasite  in  man  dur- 
ing its  larval  stage  is  Porocephalus 
nrmillatus  (Fig.  148).  Unlike  Lingua- 
tula, this  worm  has  a  cylindrical  body, 
only  about  18  to  22  rings  of  segments 
and  a  total  length  of  about  one-half 
an  inch.  The  segments  have  no  fine 
denticulations  as  they  have  in  Lingua- 
tula. This  species  is  said  to  spend  its 
adult  life  in  the  lungs  of  the  African  python,  the  larvae  occurring 
occasionally  in  man,  but  more  frequently  in  giraffes,  monkeys  and 
other  African  animals.     Sambon  thinks  the  eggs  escape  from  the 


Fig.  148.  Porocephalus  armil- 
latus;  9'  female;  $,  male. 
Natural  size.     (After  Sambon.) 


POROCEPHALUS  351 

nostrils  of  pythons  into  water,  and  that  infection  occurs  through 
drinking.  The  return  of  the  larva  from  the  intermediate  host 
to  the  python  probably  takes  place  by  the  intermediate  host 
being  eaten.  The  larvae  as  they  occur  in  man  or  other  animals 
may  either  be  encysted  or  freely  migrating  in  the  tissues  or  body 
cavities.  Such  symptoms  as  emaciation,  bronchitis,  pleurisy  and 
offensive  discharges  from  the  lungs  may  be  present.  From  75 
to  100  larvae  have  been  known  to  be  expectorated  by  a  single 
patient.  Recently  Mouchet  reports  finding  Porocephalus  in  over 
22  per  cent  of  post  mortem  examinations  made  at  Leopoldville, 
in  Belgian  Congo. 

A  more  slender  species,  P.  moniliformis,  bright  yellow  in  color, 
occurs  as  an  adult  in  pythons  in  southern  Asia  and  the  East 
Indies,  and  in  two  cases  human  infection  has  been  reported. 
One  case  of  human  infection  with  a  Porocephalus  in  Montana  in 
1876  is  of  interest,  since,  as  pointed  out  by  Sambon,  it  may  have 
been  the  larva  of  P.  crotali  of  rattlesnakes. 


CHAPTER  XXI 
TICKS 

While  mites  as  a  group  are  extremely  annoying  pests,  with  one 
exception  they  are  not  dangerous  as  disease  carriers.  The  ticks, 
on  the  other  hand,  are  not  only  annoying  but  dangerous.  Several 
important  diseases  of  domestic  animals  are  transmitted  solely  by 
ticks,  and  several  human  diseases  are  likewise  dependent  on 
ticks  for  dissemination,  especially  African  relapsing  fever  or 
*'  tick  fever  "  and  Rocky  Mountain  spotted  fever.  In  addition 
to  this,  tick  bites,  at  least  those  of  some  species,  give  rise  to  a 
serious  form  of  paralysis,  especially  in  children,  which  may  end 
in  death.  Tick  bites  also  frequently  give  rise  to  dangerous 
ulcerating  sores  which  may  result  in  fatal  blood  poisoning.  The 
economic  importance  of  ticks  as  parasites  of  domestic  animals  is 
not  for  consideration  here,  but  it  would  not  be  amiss  to  state 
that  the  annual  loss  in  the  United  States  from  cattle  ticks  alone 
is  estimated  at  from  $40,000,000  to  $50,000,000.  It  is  evident 
that  ticks  should  be  looked  upon  as  worthy  candidates  for  ex- 
termination wherever  this  is  possible. 

Although  the  ticks  constitute  only  one  of  several  divisions  of 
the  order  Acarina,  they  are  so  readily  distinguishable  and  so 
well  known  that  in  the  popular  mind  the  ticks  are  looked  upon  as 
a  group  quite  distinct  from  all  other  mites,  and  equivalent  with 
them.  They  are  of  relatively  large  size  and  usually  exceed  all 
other  Acarina  in  this  respect  even  in  their  larval  stages.  Some 
species  when  full  grown  and  engorged  are  fully  half  an  inch  in 
length. 

General  Anatomy.  —  The  body  of  a  tick  is  covered  by  a 
leathery  cuticle  which  is  capable  of  great  expansion  in  the  fe- 
males as  they  engorge  themselves  on  their  host's  blood,  fiUing  the 
numerous  complex  pouches  of  the  digestive  tract  (Fig.  149). 
When  not  engorged  ticks  are  flat  and  oval  or  triangular  in  shape 
(Fig.  154),  usually  tapering  to  the  anterior  end,  but  after  en- 
gorgement they  resemble  beans  or  nuts  of  some  kind  (Fig.  158). 

352 


GENERAL  STRUCTURE 


353 


Fig.  149.  Digestive  tract  of  Argas  persicus;  an.,  anus;  ch.,  chelicera;  int.  c, 
intestinal  coeca;  oes.,  oesophagus;  ph.,  pharynx;  sal.  gl.,  salivary  glands;  st. 
stomach.      X  about  20.     (Adapted  from  Robinson  and  Davidson.) 


.-  ^yp- 


-cbcl. 


bas.  p. 


Fig.  150.  Head  or  capitulum  of  tick; 
hyp.,  hypostome;  chel.,  chelicera;  pal., 
palpus;  bas.  p.,  basal  piece.  (Partly  after 
Banks.) 


Fig.  151.  Tip  of  chelicera  of  a  tick, 
much  enlarged;  cut.  p.,  articulated 
cutting  part;  shaft,  shaft;  sh.,  sheath; 
fi.  t.,  tendon  of  flexor  muscle;  ex.  t., 
tendon  of  extensor  muscle.  (After 
Nuttall,  Cooper  and  Robinson.) 


354 


TICKS 


Most  ticks  have  a  little  shield  or  "  scutum  "  on  the  dorsal  sur- 
face, quite  small  in  the  females,  but  nearly  or  quite  covering  the 
back  in  the  males  (Fig.  156).  Attached  to  it  in  front  is  a  little 
triangular  piece,  the  capitulum  or  "  head "  which  bears  the 
mouthparts  (Fig.  150).  The  latter  consist  of  a  quite  formidable 
piercing  organ,  the  hypostome,  a  pair  of  chelicerse  or  mandibles 
which  are  armed  with  hooks  (Fig.  151),  and  a  pair  of  blunt  palpi 
which  are  probably  tactile  in  function.  The  hypostome  is  a 
rasplike  structure,  beset  with  row  after  row  of  recurved  teeth 
(Fig.  152).     So  firmly  do  these  hold  in  the  flesh  into  which  the 

proboscis  is  inserted  that 
forcible  removal  of  a  tick 
often  results  in  the  tearing 
off  of  the  body  from  the 
capitulum  which  remains  at- 
tached to  the  host.  Like 
other  Arachnida,  ticks  have 
four  pairs  of  legs.  These 
are  quite  conspicuous  when 
the  body  is  empty  but  are 
^  hardly  noticeable  after  en- 
gorgement. The  breathing 
ticro'S«''^^r*ZrJo™f^J;.«:  apparatus  consists  of  a  sys- 

nymph;   B,  Argas  persicus,  adult;   C,  Ixodes    tem   of   tracheffi   which    open 

7^\:^!Zt^l  SZ.rt^.  by  a  pair  of  spiracles  in  the 

male;    G,  Omithodorus  mouhata,  nymph;   H,    vicinity    of    the    fourth    pair 

r^a*:^TuenhS;:rN^u;ifr'^'"  ^f  l«g«-     The  shape  of  the 

plates  which  cover  the  spir- 
acles are  sometimes  used  in  distinguishing  species.  The  ventral 
surface  has  two  openings,  the  genital  pore  just  back  of  the  pro- 
boscis, and  the  anus  some  distance  from  the  posterior  end  of  the 
body  (Fig.  154). 

Habits  and  Life  History.  —  All  ticks  are  parasitic  during  some 
part  of  their  lives.  The  majority  of  them  infest  mammals, 
though  many  species  attack  birds  and  some  are  found  on  cold- 
blooded animals.  A  very  decided  host  preference  is  shown  by 
some  species,  whereas  others  appear  to  be  equally  content  with 
any  warm-blooded  animal  which  comes  their  way.  In  many 
species  the  hosts  or  parts  of  hosts  selected  by  the  adults  are  not 
the  same  as  those  selected  by  the  immature  forms. 


V 


LIFE  HISTORY  355 

The  life  histories  of  all  ticks  are  more  or  less  similar.  After 
several  days  of  mating  the  female  ticks  engorge  and  soon  after 
drop  to  the  ground  and  begin  to  lay  their  eggs  (Fig.  153).  These 
are  deposited  on  or  just  under  the  surface  of  the  ground.  Some 
of  the  family  Argasidae  engorge  several  times,  laying  a  batch  of 
from  20  to  50  eggs  after  each  gluttonous  repast.  All  of  the 
Ixodidse,  on  the  other  hand,  lay  their  eggs  after  a  single  engorge- 
ment. The  eggs  number  from  a  few  hundred  in  some  species 
to  upwards  of  10,000  in  others  and  are  laid 
in  rather  elongate  masses  in  front  of  the 
female.  Each  egg  as  it  is  passed  out  by  the 
ovipositor  is  coated  with  a  viscid  substance 
by  glands  between  the  head  and  dorsal  shield 
of  the  tick  and  is  then  added  to  the  mass  in 
front.  The  process  of  egg-lajdng  occupies 
several  days,  as  not  more  than  several  hun- 
dred eggs  can  be  passed  out  and  treated 
with  the  viscid  coating  in  the  course  of  a 
day. 

The  eggs  develop  after  an  incubation  p>eriod 
which  varies  with  the  temperature  from  two      -pia     153       Texas 
or  three  weeks  to  several  months.     Eggs  de-  fever  tick,  Margaropus 
posited  in  the  fall 'do  not  hatch  until  the  fol-  (^tt^Grkybi^^^^ 
lowing  spring. 

The  larval  ticks  which  hatch  from  the  eggs  are  much  smaller 
than  the  adult  ticks  and  have  only  six  legs  (Fig.  157B).  They  are 
popularly  known  as  "  seed  ticks."  The  seed  ticks  soon  after 
hatching  climb  up  on  a  blade  of  grass  or  bit  of  herbage  and  assume 
a  p>oUcy  of  watchful  waiting  until  some  suitable  host  passes  with- 
in reach.  Seed  ticks  must  be  imbued  with  almost  unlimited 
patience,  since  in  many  if  not  in  the  majority  of  cases  long  delays 
must  fall  to  their  lot  before  a  suitable  host  comes  their  way  like 
a  rescue  ship  to  a  stranded  mariner.  The  jarring  of  a  footstep 
or  rustle  of  bushes  causes  the  ticks  instantly  to  stretch  out  to 
full  length,  feeling  with  their  clawed  front  legs,  eager  with  the 
excitement  of  a  life  or  death  chance  to  be  saved  from  starvation. 
If  success  rewards  their  patience,  even  though  it  may  be  after 
many  days  or  weeks,  they  feed  for  only  a  few  days,  becoming 
distended  with  blood,  and  then  drop  to  the  ground  again.  Re- 
tiring to  a  concealed  place  they  rest  for  a  week  or  more  while 


356  TICKS 

they  undergo  internal  reorganization.  Finally  they  shed  their 
skins  and  emerge  as  eight-legged  but  sexually  immature  ticks 
known  as  nymphs  (Fig.  157C).  The  nymphs  climb  up  on  bushes 
or  weeds  and  again  there  is  a  period  of  patient  waiting,  resulting 
either  in  starvation  or  a  second  period  of  feasting.  Once  more 
the  ticks  drop  to  the  ground  to  rest,  transform  and  moult,  this 
time  becoming  fully  adult  and  sexually  mature.  In  this  condition 
a  host  is  awaited  for  a  third  and  last  time,  copulation  takes  place, 
sometimes  even  before  a  final  host  is  reached,  and  the  females 
begin  their  final  gluttonous  feeding  which  results  in  distending 
them  out  of  all  proportions.  In  some  species,  especially  those 
which  live  on  hosts  which  return  to  fixed  lairs,  copulation  takes 
place  ojff  the  host.  When  this  occurs,  as  in  many  species  of 
Ixodes,  the  male  is  often  not  parasitic  at  all,  and  may  differ 
markedly  from  the  female  in  the  reduced  structure  of  its  hypo- 
stome  (Fig.  152C,  E  and  F).  In  all  species  the  males  die  shortly 
after  copulation. 

This,  in  general,  is  the  life  history  of  ticks,  but  it  is,  of  course, 
subject  to  considerable  variation  in  different  species.  In  many 
species  there  are  two  nymphal  periods  instead  of  one.  In  some 
species,  as  in  the  Texas  fever  tick,  Margaropus  annulatus,  the 
moulting  takes  place  directly  on  the  host,  thus  doing  away  with 
the  great  risk  of  being  unable  to  find  a  new  host  after  each  suc- 
cessive moult.  In  a  few  species  the  first  moult  is  passed  through 
on  the  host,  but  the  second  is  passed  on  the  ground.  The  most 
important  asset  of  ticks  to  counterbalance  the  disadvantage  of 
having  to  find  new  hosts  is  their  extraordinary  longevity.  Larvae 
of  ticks  have  been  known  to  live  more  than  six  months  without 
food,  and  adults  have  been  kept  alive  in  corked  vials  for  five 
years. 

There  are  two  families  of  ticks,  the  Argasidse  and  the  Ixodidse. 
The  Argasidse  include  the  bird  ticks  and  their  allies,  which  are 
distinguished  from  the  Ixodidse  by  the  absence  of  a  dorsal  shield 
and  in  having  the  head  partially  or  entirely  concealed  under  the 
overlapping  anterior  margin  of  the  body  (Fig.  154).  The  fe- 
males of  this  family  do  not  become  distended  as  do  those  of  the 
Ixodidse,  but  take  more  moderate  though  more  frequent  meals. 
They  are  chiefly  inhabitants  of  warm  countries.  Both  nymphs 
and  adults  feed  at  night,  usually  dropping  off  their  hosts  im- 
mediately after  a  meal,  and  thus  seldom  being  carried  from  the 


TICK  BITES 


367 


lairs  or  abodes  of  their  hosts.  The  Ixodidae,  on  the  other  hand, 
inhabit  the  hosts  rather  than  their  lairs,  and  frequently  remain 
attached  for  several  days,  or  even  longer.  In  the  less  capacious 
Argasidae  the  females  lay  their  eggs  in  a  number  of  installments 


Fig.  154.  Comparison  of  dorsal  and  ventral  view  of  Ixodid  and  Argasid  females; 
A,  dorsal  view  of  Ixodid  9  I  ^' ■>  ventral  view  of  same;  B,  dorsal  view  of  Argasid 
9  ;  B' ,  ventral  view  of  same.  An.,  anus;  cap.,  capitulum;  d.  sh.,  dorsal  shield; 
e.s.,  eye  spot;   gen.  op.,  genital  opening;   sp.,  spiracle. 


after  successive  feeds,  and  the  total  number  of  eggs  may  be 
counted  in  hundreds  instead  of  thousands.  The  reason  for  this 
difference  is  readily  accounted  for  by  the  difference  in  habits  in 
the  two  families,  since  the  progeny  of  the  Argasidae,  reared  in 
the  lairs  of  the  hosts,  have  far  better  chances  of  finding  a  host  and 
of  surviving  than  do  the  progeny  of  the  Ixodidae  which  live  on 
their  hosts  and  may  drop  off  to  lay  their  eggs  almost  anywhere 
in  the  wanderings  of  the  host. 

Tick  Bites.  —  The  status  of  ticks  as  human  parasites,  as  stated 
before,  is  one  not  to  be  passed  over  lightly.     Aside  from  the 


358  TICKS 

transmission  of  diseases  tick  bites  are  dangerous  to  man  in  a 
number  of  ways. 

The  wounds  made  by  ticks,  especially  if  the  head  is  torn  off  in 
a  forcible  removal  of  the  parasite,  are  very  likely  to  become 
infected  and  result  in  inflamed  sores  or  extensive  ulcers,  not  in- 
frequently ending  in  blood  poisoning.  The  author,  as  the  result 
of  the  bite  of  a  tick  in  northern  California  (probably  Dermacentor 
occidentalis) ,  suffered  from  an  ulcerating  sore  on  his  arm,  over  half 
an  inch  in  depth  and  three-fourths  of  an  inch  in  diameter.  Blood 
poisoning  set  in  early  causing  a  very  high  temperature  and  great 
pain  in  the  arm,  and  it  was  only  a  timely  return  to  civilization 
and  hospital  care  that  saved  his  arm  if  not  his  life.  Sanitary 
removal  of  ticks  and  cleansing  of  the  wounds,  as  described  on 
p.  367,  would  be  well  worth  the  consideration  of  every  inhabitant 
or  traveller  in  a  tick-infested  country. 

Tick  Paralysis.  —  More  serious  than  the  painful  wound  made 
by  ticks  is  a  peculiar  paralyzing  effect  of  tick  bites,  known  as 
tick  paralysis.  This  occurs  especially  from  tick  bites  on  the  back 
of  the  neck  or  on  the  head;  it  affects  the  legs  first,  but  spreads 
forward  in  a  few  days  to  the  arms  and  neck  and  may  result  in 
death.  Paralysis  in  man  and  animals  from  tick  bites  has  been 
reported  from  South  Africa  and  Australia  and  in  North  America 
from  the  parts  of  Oregon  and  British  Columbia  inhabited  by  the 
spotted  fever  tick.  Sheep  are  especially  subject  to  tick  paraly- 
sis, to  such  an  extent  in  British  Columbia  as  to  present  a  serious 
problem.  This  peculiar  effect  of  tick  bites  has  been  reproduced 
experimentally  in  sheep  in  places  where  it  has  not  been  known 
to  occur  normally,  by  allowing  a  spotted  fever  tick,  Dermacentor 
venustus  (Fig.  156),  to  bite  along  the  spinal  column.  The  bites 
of  this  tick  are  particularly  likely  to  cause  paralysis,  though  it  is 
not  yet  known  whether  this  is  because  of  an  especially  toxic 
secretion  produced  by  this  species  or  because  of  its  preference  for 
biting  along  the  spinal  cord  or  on  the  head.  There  has  been 
much  controversy  as  to  what  really  causes  the  paralysis,  some 
authors  believing  that  it  is  due  to  a  microorganism  injected  by 
the  tick,  since  it  is  usually  six  or  seven  days  after  the  attach- 
ment of  the  tick  before  the  effect  is  felt.  The  fact,  however, 
that  no  such  organism  can  be  discovered,  that  inoculations  of 
blood  and  other  parts  of  diseased  animals  into  healthy  ones  does 
not  result  in  transmission  of  the  disease,  and  that  the  paralysis 


TRANSMISSION  OF  DISEASES  359 

is  usually  accompanied  by  little  or  no  fever,  makes  this  seem 
unlikely.  A  single  attack  of  tick  paralysis  seems  to  confer 
immunity  and  it  is  probable  that  many  children  are  naturally 
immune.  The  most  reasonable  explanation  is  that  the  ticks 
secrete  a  toxic  substance,  especially  when  rapidly  engorging, 
which  has  a  specific  action  on  the  motor  nervous  system.  Pos- 
sibly the  bite  must  pierce  or  come  in  contact  with  a  nerve  or 
nerve  ending  in  order  to  produce  the  effect. 

Numerous  cases  of  tick  paralysis  in  children  have  occurred 
in  British  Columbia  and  in  the  Blue  Mountains  of  Eastern 
Oregon.  One  doctor  in  the  vicinity  of  Pendleton  reported  no 
less  than  13  cases.  The  disease  begins  with  paralysis  of  the 
legs  and  usually  results  in  complete  loss  of  their  use;  the  paraly- 
sis ascends  in  the  course  of  two  or  three  days,  affecting  the  arms 
and  finally  the  thorax  and  throat.  Unless  the  heart  and  respi- 
ration are  affected,  recovery  follows  in  from  one  to  six  or  eight 
days  after  removal  of  the  ticks.  The  latter,  often  in  pairs,  are 
usually  found  on  the  back  of  the  neck  or  along  the  middle  line 
of  the  head,  especially  just  at  the  base  of  the  skull.  If  the  ticks 
are  not  removed,  the  disease  may  result  in  death  or  in  spon- 
taneous recovery  after  a  few  days  or  a  week. 

Unfortunately  in  most  of  the  cases  of  tick  paralysis  in  chil- 
dren the  ticks  have  not  been  identified,  but  it  is  well  known 
that  the  spotted  fever  tick  is  the  most  frequent  cause  of  paralysis 
in  sheep  and  the  only  species  by  which  such  a  disease  has  been 
reproduced  experimentally.  In  South  Africa,  however,  a  similar 
paralysis  in  sheep  results  from  the  bites  of  Ixodes  pilosus,  and 
paralysis  in  children  in  Australia  from  the  bites  of  other  but 
undetermined  species.  The  scrub-tick,  Ixodes  holocyclus,  is  said 
to  be  troublesome  as  a  cause  of  paralysis  in  young  stock  in  New 
South  Wales.  In  the  regions  of  Oregon  and  British  Columbia 
where  tick  paralysis  is  especially  prevalent  there  occur  a  number 
of  different  ticks,  and  there  is  no  evidence  that  any  tick  which 
attacks  man  along  the  spinal  cord  or  on  the  head  may  not  cause 
paralysis. 

Ticks  and  Disease 

The  r61e  of  ticks  as  disease  carriers  has  been  well  established 
since  Button  and  Todd  in  1905  proved  that  African  relapsing 
fever  was  transmitted  by  a  species  of  tick  known  as  the  tampan, 


360  TICKS 

Ornithodorus  moubata  (Fig.  155).  A  year  later  Dr.  Ricketts 
showed  that  spotted  fever  in  the  United  Stated  was  dependent 
upon  a  tick,  Dermacentor  venustus,  for  its  transmission.  It  is 
now  known  that  ticks  serve  as  intermediate  hosts  for  a  consider- 
able number  of  disease  germs  of  two  different  groups,  the  spiro- 
chaetes  and  the  Piroplasmata.  The  various  forms  of  relapsing 
fever  of  man  are  caused  by  spirochaetes,  and  it  is  possible  that 
all  the  different  types  of  this  disease  may  be  transmitted  by 
ticks,  though  in  some  of  the  types  other  arthropods  act  as  the 
usual  transmitters.  Many  diseases  of  domestic  animals  are 
caused  by  organisms  of  the  group  Piroplasmata  (see  p.  182), 
including  Texas  fever  of  cattle  in  North  America,  East  Coast 
fever  of  cattle  in  Africa,  biliary  fever  of  horses  in  Asia  and  Africa, 
and  similar  diseases  of  sheep,  dogs,  rats  and  monkeys.  The  only 
human  disease  positively  known  to  be  caused  by  an  organism 
of  this  group  is  Oroya  fever  of  Peru,  caused  by  Bartonella  hacilli- 
formis  (see  p.  178).  Whether  or  not  a  tick  is  instrumental  in 
transmitting  this  disease  is  not  yet  known.  Rocky  Mountain 
spotted  fever  was  at  one  time  thought  to  be  caused  by  a  member 
of  the  Piroplasmata,  but  the  parasite  of  this  disease  is  still  un- 
known. The  fact  that  it  is  transmitted  by  a  tick  suggests  that 
it  may  be  found  to  belong  either  to  the  spirochaetes  or  to  the 
Piroplasmata.  Ticks  have  also  been  suspected  of  carrying  the 
East  Indian  form  of  kedani  fever  which  in  Japan  is  transmitted 
by  a  larval  mite,  but  this  has  not  been  proved. 

Ticks  and  Relapsing  Fever. —  The  fact  that  tick  bites  frequently 
give  rise  to  serious  fever  and  illness,  now  known  as  relapsing 
fever,  which  not  infrequently  result  in  death,  has  been  well  known 
in  Africa  for  many  years,  in  fact  Livingston  in  his  "  Darkest 
Africa  "  speaks  of  this  disease  as  resulting  from  tick  bites.  The 
implicated  ticks,  Ornithodorus  moubata,  known  as  "  tampans  "  or 
'' carapatos,"  are  very  common  pests  in  shaded  places  in  the 
dirty  thatched  houses  of  the  natives,  and  are  difficult  to  avoid. 
They  occur  chiefly  along  the  routes  of  travel,  being  readily 
carried  and  dispersed  by  caravans.  They  live  also  in  the  bur- 
rows of  warthogs.  A  detailed  account  of  the  role  played  by 
the  tick  in  harboring  and  transmitting  relapsing  fever  spiro- 
chaetes and  a  description  of  the  disease  can  be  found  in  Chap. 
IV,  p.  42. 

The  tampan  is  a  broad  oval  tick   (Fig.   155),   mud-colored, 


DERMACENTOR  VENUSTUS  361 

about  five-eighths  of  an  inch  in  length,  belonging  to  the  family 
Argasidse.  Like  the  other  members  of  the  family  it  has  no 
dorsal  shield  and  has  the  margin  of  the  body  produced  in  such 
a  way  as  to  conceal  most  of  the  head  and  legs.  Unlike  most 
ticks  the  larvae  are  weak  and  do  not  feed 
but  transform  to  nymphs  very  soon  after 
the  eggshell  splits.  The  nymphs  are 
said  to  produce  more  painful  wounds  than 
the  adults  and  they  can  just  as  readily 
transmit  relapsing  fever. 

An  allied  species,  0.  savignyi,  occurs 
from  Abyssinia  through  Arabia  to  India 
and  Ceylon  and  attacks  man,  camels  and 
horses.      It  is  said  to  transmit  the  Indian 

-  !•       1         •         c  •      i  1  i    •  Fig.   155.     The  tampan, 

form  of  relapsmg  fever  m  these  countries,  omithodorus  mouhata.  x  3. 
Like  0.  mouhata  it  attacks  its  host  in  its 

resting  place,  hiding  in  the  daytime  in  dust  or  sand  in  or  around  the 
squalid  huts  of  the  natives.  Except  in  coastal  towns,  where  it  is 
abundant  everywhere,  it  is  found  chiefly  in  camps  of  long  stand- 
ing inhabited  by  men  and  animals.  Burrowing  to  a  depth  of  an 
inch  in  dusty  soil  it  can  live  without  food  for  months.  In  Persia 
0.  tholosani  is  said  to  transmit  African  relapsing  fever  which  has 
been  introduced  there.  0.  talaje  of  Mexico  and  Central  America 
has  habits  very  similar  to  those  of  the  tampan  in  Africa;  it  fre- 
quently occurs  in  the  adobe  houses  and  attacks  the  occupants 
at  night.  0.  turicata,  the  '^carapato"  of  Central  America,  is 
another  very  annoying  species.  Its  bites  are  so  severe  that  hogs 
are  said  to  have  been  killed  in  a  single  night  by  its  attacks. 
Though  not  proved  it  is  very  probable  that  one  or  both  of  these 
species  may  be  instrumental  in  transmitting  the  milder  American 
form  of  relapsing  fever.  It  is  almost  certain  also  that  another 
tick,  the  "  miana  bug  "  of  Persia,  is  capable  of  transmitting 
European  relapsing  fever  (see  p.  364). 

Ticks  and  Spotted  Fever.  —  The  tick  which  is  responsible  for 
the  transmission  of  Rocky  Mountain  spotted  fever  (see  p.  191) 
is  a  wood  tick,  Dermacentor  venustus  (andersoni)  (Fig.  156).  This 
is  a  handsome  reddish  brown  species,  the  male  of  which  has  the 
whole  back  marked  with  black  and  silvery-white  lines,  while 
the  female  has  only  the  small  dorsal  shield  marked  with  silver, 
the  abdomen  being  deep  reddish  brown.     This  species  is  one 


362 


TICKS 


which  requires  two  different  hosts  to  complete  the  Ufe  cycle. 
The  six-legged  larvae  (Fig.  157B),  of  which  there  are  about  5000 
in  a  brood,  attach  themselves  to  any  of  the  rodents  which  abound 


Fig.  156.     Spotted  fever  tick,  Dermaeentor  venustus,  male  {$)  and  female  (9)- 

Xl2. 


Fig.  157.     Development  of  spotted  fever  tick,  Dermaeentor  venustus;    A,  eggs; 
B,  larva;   C,  nymph.      X  30. 

in  the  country  where  the  ticks  occur,  especially  squirrels  of 
various  kinds.  Usually  the  larvae,  and  the  nymphs  also,  attach 
themselves  about  the  head  and  ears  of  their  host.  After  a  few 
days  the  larvae  drop,  transform  into  nymphs  (Fig.  157C)  and 


TRANSMITTERS  OF  SPOTTED  FEVER 


363 


again  attack  their  rodent  hosts.  After  dropping  off  these  and 
transforming  into  adults  they  no  longer  pay  any  attention  to  the 
rodents  but  seek  larger  animals,  especially  preferring  horses  and 
cattle,  though  they  readily  attack  other  large  wild  and  domestic 
animals  and  man.  Their  original  wild  hosts  were  probably  the 
mountain  goats,  elk  and  other  wild  game  of  the  region,  but  with 
the  supplanting  of  these  by  domestic  animals  the  latter  have 
become  the  main  host  animals  of  the  ticks.  Unlike  most  ticks, 
this  species  may  take  two  or  even  two  and  a  half  years  to  com- 
plete its  life  cycle  under  unfavor- 
able conditions.  The  winter  is 
passed  in  either  the  nymphal  or 
adult  stages. 

Dermacentor  venustus  is  found  in  a 
limited  area  in  northwestern  United 
States  and  British  Columbia,  east 
to  eastern  Montana  and  eastern 
Wyoming,  west  to  the  Cascade 
Mountains  and  south  into  Nevada 
and  Colorado.  This  distribution 
somewhat  exceeds  the  present  dis- 
tribution of  spotted  fever  (Fig.  58, 
p.  191). 

Several   different  species  of  ticks      fig.  158.    Spotted  fever  tick, 

have  been    found    capable    of    trans-    Dermacentor    venustus;     engorged 

mitting  spotted   fever  from   rodent 

to  rodent  under  experimental  conditions.  Several  species  of  ticks 
other  than  D.  venustus  are  found  in  the  spotted  fever  districts, 
but  none  of  these  can  have  any  hand  in  the  transmission  of  the 
disease  to  man  since  they  do  not  attack  him.  A  tick  closely 
related  to  D.  venustus,  the  Pacific  wood  tick,  D.  occidentalis,  oc- 
curs west  of  the  Cascades  and  Sierras  in  Oregon  and  California 
and  frequently  attacks  man.  There  is  little  doubt  but  that  if 
spotted  fever  once  got  a  foothold  in  the  territory  occupied  by  this 
tick,  the  latter  would  act  as  an  efficient  disseminator.  In  southern 
and  eastern  states  other  ticks  which  attack  man  would  probably 
disseminate  the  disease  were  it  once  introduced.  For  this  reason 
it  is  of  the  utmost  importance  that  the  infection  should  not  be 
carried  to  parts  of  the  country  which  are  not  now  infected. 
Measures  for  the  prevention  of  this  are  discussed  in  Chapter  X, 
under  '*  Spotted  Fever." 


364 


TICKS 


Other  Troublesome  Ticks 

Although  there  are  a  large  number  of  species  of  ticks  which 
will  attack  man,  there  are  a  few  in  addition  to  the  disease-causing 
species  named  above  which  deserve  special  mention  on  account 
of  the  particularly  bad  effects  of  their  bites.  The  family  Argasidse 
includes  a  number  of  species  which  produce  very  venomous  bites 
when  they  attack  man.  The  various  species  of  Ornithodorus, 
some  of  which  have  already  been  mentioned  as  carriers  of  relap- 
sing fever,  produce  very  painful  bites.  Another  species  worthy 
of  mention  is  the  famous  "  miana  bug,"  Argas  persicus  (Fig.  159), 
which  is  especially  renowned  in  Persia,  but  which  also  occurs  in 

many  other  parts  of  the  Old 
World.  This  species  is  often  a 
great  tormentor  of  human  be- 
ings, especially  in  dirty  huts 
where  it  can  breed  readily.  It 
is  primarily,  however,  a  parasite 
of  fowls,  and  is  believed  to  be 
identical  with  the  American  fowl 
tick,  Argas  miniatus.  The  bites 
of  the  miana  bug  are  dreaded 
not  only  on  account  of  their 
painfulness,  but  also  because 
they  are  believed  to  be  a  means 
of  transmission  of  European  re- 
FiG.    159.      Persian   tick   or  fowl  lapsing  fever,  in  common  with 

tick,     Argas    persicus.        X  5.       (After    ,.  ,  ,  -i  •  j_ 

Braun.)  lice  and  perhaps  other  msects. 

A  closely  allied  species,  A.  re- 
flexus,  is  a  common  parasite  of  pigeons  in  Europe  and  North 
Africa,  and  frequently  attacks  people  who  come  in  contact  with 
infested  birds  or  cotes. 

Another  argasid  tick  which  deserves  special  mention  is  the 
"  pajaroello,"  0.  coriaceus  of  California.  Herms  states  that 
"  natives,  principally  Mexicans,  in  the  vicinity  of  Mt.  Hamilton 
fear  this  parasite  more  than  they  do  the  rattlesnake,  and  tell 
weird  tales  of  this  or  that  man  having  lost  an  arm  or  leg,  and  in 
one  instance  even  death  having  ensued,  as  a  result  of  a  bite  by 
the  Pajaroello.  There  seems  to  be  a  suspicion  in  that  region 
that  three  bites  will  result  in  certain  death.     The  stories  all 


SPINOSE  EAR  TICK 


365 


agree  in  the  essential  detail  that  the  bite  results  in  an  irritating 
lesion  which  is  slow  to  heal  and  often  leaves  an  ugly  deep  scar." 
The  tick  is  about  two-fifths  of  an  inch  in  length,  irregularly  oval, 
with  thick  turned-up  margins,  roughly  shagreened,  and  of  a 
yellowish  earthy  color  spotted  rusty  red.  It  occurs  in  the  Coast 
Range  mountains  of  California  and  in  Mexico  and  according  to 
Herms  is  most  commonly  found  in  the  dry  leaves  under  live 
oak  trees  where  cattle  or  other  animals  are  accustomed  to  lie 
in  the  shade.  It  passes  through  from  four  to  seven  moults  to 
reach  the  adult  state,  occupying 
from  one  to  two  years  to  com- 
plete its  life  history,  according 
to  its  success  in  finding  suitable 
hosts.  The  bites  of  this  tick 
produce  sharp  pain,  accompanied 
by  a  considerable  discoloration 
around  the  wound,  and  if  on  an 
arm  or  leg  the  whole  limb  may 
become  greatly  swollen  as  in  the 
case  of  a  snake  bite.  After  scab- 
bing over,  the  wound  may  con- 
tinue to  exude  lymph  and  to  be 
irritable  for  several  weeks,  and  it 
is  possible  that  infection  and  con- 
sequent blood-poisoning  might 
readily  occur,  thus  giving  a  basis 
for  the  tales  mentioned  above.  ^^^  (ofo^SSL,°U- 

Another  noteworthy  member  of  nini.     x  lo.     (After  Marx  from 
the   Argasidae   is   the   spinose    ear 

tick,  Otiobius  (or  Ornithodorus)  megnini  (Fig.  160),  of  south- 
western United  States  and  Mexico,  and  now  becoming  common 
in  parts  of  South  Africa.  It  is  very  troublesome  to  man  as  well 
as  to  horses  and  other  domestic  animals.  The  nymphs,  which 
develop  from  the  larvae  in  the  ears  of  their  hosts,  are  peculiar  in 
having  very  spiny  bodies,  quite  different  from  the  smooth  larvae 
and  adults.  The  nymphs  remain  attached  to  their  hosts  for 
months  but  finally  drop  off  to  transform  into  adults.  The 
adults  are  not  parasitic  but  lay  their  eggs  without  further  feed- 
ing. The  pain  and  annoyance  caused  by  the  spiny  nymphs  in 
the  ears  of  domestic  animals  is  sufficient  to  cause  them  to  be- 


366 


TICKS 


come  ill-tempered  and  emaciated.  Children  sometimes  suffer 
a  great  deal  from  their  attacks,  and  have  difficulty  in  dislodging 
the  invaders  from  their  ears.  This  can  readily  be  done,  however, 
by  pouring  olive  oil  or  some  other  harmless  oil  into  the  ears. 

Although  there  are  a  large  number  of  species  of  the  family 
Ixodidae  which  may  attack  man,  they  do  not  as  a  rule  prove  as 
great  pests  or  produce  as  severe  bites  as  some  of  the  Argasidse. 
The  characteristics  of  some  of  the  principal  genera  are  given  in 


F 

Fig.  161.     Diagrams  of  rostra  or  capitula  of  important  genera  of  Ixodid  ticks, 
useful  in  identification.     (After  Nuttall.) 

With  long  rostrum  Other  characteristics 

A,  Ixodes Anal,  groove  in  front  of  anus,  no  eyes, 

no  festoons. 

B,  Hyalomma eyes  present,  festoons  present. 

C,  Amblyomma eyes  present,  festoons  present,  ornate. 

or 
Aponomma eyes  absent,  festoons  present,  ornate. 

With  short  rostrum 

D,  Haemaphysalis eyes  absent. 

E,  Margaropus circular  spiracles. 

F,  Rhipicephalus  .  .  .■ comma-shaped  spiracles. 

G,  Dermacentor eyes  present,  ornate. 

Fig.  161  and  accompanying  table.  Only  a  few  species  need 
special  mention  here.  Dermacentor  venustus  is,  of  course,  of 
preeminent  importance  on  account  of  its  role  as  a  transmitter 
of  spotted  fever  and  in  producing  tick  paralysis.  D.  occidentalism 
the  ''  wood  tick  "  of  the  Pacific  slope  of  the  United  States,  is 
another  member  of  the  genus  which  very  commonly  attacks  man; 
its  bites  are  particularly  likely  to  cause  ugly  ulcerating  sores. 
Experimentally,  as  said  before,  it  has  been  shown  to  be  capable  of 
transmitting  spotted  fever,  and  it  would  probably  act  as  an  effi- 


TREATMENT  OF  BITES  367 

cient  disseminator  if  the  disease  were  introduced  into  its  terri- 
tory. The  same  might  be  said  of  D.  variabilis,  the  dog  tick  of 
eastern  North  America,  though  this  species  less  commonly 
attacks  man. 

Of  particular  interest  is  the  effect  produced  by  the  larvae  of 
certain  ticks  in  southeastern  Africa,  especially  the  bont  tick, 
Amhlyomma  hebrceum.  Its  larvae  produce  itching  and  painful 
wounds  which  may  be  followed  in  a  week  or  so  by  fever,  head- 
ache, skin  eruptions  and  other  general  symptoms.  The  name 
*'  tick-bite  fever  "  has  been  applied  to  this  malady.  Whether  it 
is  caused  by  a  microorganism  is  unknown.  Immunity  rapidly 
develops,  so  that  usually  only  new  arrivals  are  affected.  In 
Europe  one  of  the  most  troublesome  species  of  Ixodidae,  as  far 
as  man  is  concerned,  is  the  common  dog  tick,  Ixodes  ricinis, 
which  attacks  a  great  variety  of  animals,  and  is  evidently  quite 
fond  of  human  blood.  A  particularly  obnoxious  species  in 
tropical  America  is  Amhlyomma  cajennense.  Not  only  the 
nymphs  and  adults  but  also  the  larvae  of  this  species  are  pests 
of  man. 

Treatment  and  Prevention.  —  As  shown  above  tick  bites  may 
be  attended  by  a  number  of  serious  results,  such  as  fever,  ulcer- 
ating sores,  paralysis  or  disease  transmission.  The  treatment 
of  the  bites,  therefore,  may  be  of  considerable  importance.  It 
has  been  shown  that  ticks,  at  least  in  the  case  of  the  relapsing 
fevers,  do  not  ordinarily  infect  directly  by  biting,  but  by  con- 
taminating the  wound  with  infected  excrement.  It  is  obvious, 
therefore,  that  disinfection  of  the  wound  after  removal  of  the 
tick  would  be  a  precaution  of  great  value  in  places  where  ticks 
carry  diseases  to  which  human  beings  are  susceptible.  Such 
treatment  would  also  prevent  bacterial  infections  of  various 
kinds  from  entering  the  wounds  and  causing  ulceration  or  blood- 
poisoning. 

Ticks  should  never  be  removed  forcibly  since  if  so  handled 
the  head  is  likely  to  tear  off  from  the  body  and  remain  in  the 
wound,  held  there  by  the  ugly  barbed  proboscis.  A  drop  of 
kerosene,  creoline  or  some  other  oil  on  the  head  of  the  tick  will 
cause  it  to  withdraw  its  beak  and  drop  off  in  the  course  of  a 
minute  or  two.  Disinfection  of  the  wound  with  alcohol,  weak 
carbolic,  lysol  or  other  disinfecting  agent  should  follow  imme- 
diately. 


368  TICKS 

Precautions  against  tick  bites  where  serious  diseases  are  likely 
to  result  are  of  the  greatest  importance  but  very  difficult.  King, 
while  investigating  spotted  fever,  spent  a  whole  season  in  the 
heart  of  the  Bitter  Root  Valley  in  Montana  where  spotted  fever 
infection  was  most  dangerous.  He  wore  high-topped  shoes  and 
cotton  outer  garments  soaked  in  kerosene  and  had  pieces  of 
khaki  cloth  soaked  in  kerosene  sewed  to  the  tops  of  his  boots  or 
fastened  by  drawstrings  higher  up  on  his  leg.  A  leg  covering  of 
oil-proof  material  with  crude  oil  applied  on  the  outside  would 
be  of  benefit,  according  to  King.  In  Abyssinia  the  attacks  of 
Ornithodorus  savignyi  are  prevented  by  rubbing  the  feet  with 
turpentine. 

Means  of  control  of  tick  pests  vary  considerably  with  the  dif- 
ferent species,  depending  on  the  hosts,  their  seasonal  history, 
their  varying  life  histories  and  other  factors. 

Most  of  the  species  of  ticks  which  attack  man  are  normally 
parasitic  on  domestic  animals,  and  therefore  means  of  extermi- 
nating ticks  on  the  latter  would  tend  to  reduce  the  human  pests. 

Ticks  on  domestic  animals  may  be  destroyed  either  by  hand 
treatment  or  by  dipping,  or  by  the  elimination  of  ticks  from 
pastures  by  starvation.  The  cattle  tick,  Margaropus  annulatus, 
has  been  eliminated  from  many  ranches  by  a  skillful  manoeuvering 
of  the  cattle,  driving  them  from  field  to  field  in  such  a  way  that 
in  the  course  of  a  number  of  months  the  ticks  would  all  have 
dropped  and  perished  from  starvation.  Such  a  plan  is  not 
feasible  for  many  species  since  a  variety  of  hosts  may  be 
utilized,  and  long  periods  of  starvation  can  be  endured  without 
injury. 

Dipping  of  infested  animals  is  a  good  control  method.  An 
arsenical  dip  has  been  found  best  adapted  for  destruction  of 
ticks  on  their  hosts,  a  description  of  which,  with  me^ods  of 
preparing  and  using,  is  given  in  Farmers'  Bulletin  lIH^.  378 
of  the  U.  S.  Department  of  Agriculture. 

Hand  treatment  with  arsenical  dip  by  means  of  rags,  mops  or 
sprays  is  sometimes  found  more  practical. 

The  systematic  dipping  of  domestic  animals  in  the  spotted 
fever  districts  of  Montana  for  a  period  of  three  years  has  been 
recommended  by  the  U.  S.  Department  of  Agriculture  for  the 
elimination  of  the  spotted  fever  tick  from  these  regions.  In 
this  particular  case  supplemental  means  of  control  consist  in  the 


CONTROL  369 

destruction  of  indigenous  rodents  in  a  wholesale  manner,  and 
the  clearing  away  of  brush  land  in  tick-infested  areas. 

Another  means  of  destruction  of  spotted  fever  ticks  has  been 
found  in  grazing  sheep  on  tick-infested  lands.  Range  sheep  have 
been  found  to  destroy  ticks  in  large  numbers  by  the  ticks  becom- 
ing entangled  in  the  wool  and  starved.  Five  hundred  sheep  were 
found  to  destroy  25,000  ticks  in  a  season. 

Ticks  which  infest  the  lairs  of  their  hosts,  attacking  only  at 
night  and  for  brief  periods,  can  be  more  easily  handled.  In 
this  case  thorough  disinfection  by  fumigation  or  by  spraying 
with  a  disinfectant,  and  thorough  cleanliness  in  stalls,  coops, 
kennels,  huts  or  other  host  homes  will  effectually  destroy  them. 
The  disease-carrying  tampan,  Ornithodorus  mouhata,  of  Africa  is 
an  example  of  a  tick  which  can  be  controlled  by  such  methods. 
Dirty,  poorly  kept  native  huts  are  the  ideal  habitats  for  tampans, 
which  secrete  themselves  during  the  day  in  crevices,  thatched 
roofs  or  debris,  after  the  manner  of  bedbugs.  Plastering  houses 
with  mud,  building  of  smudges,  fumigation  and  cleanliness  are 
methods  which  usually  succeed  in  keeping  out  ticks.  Crevices, 
bed  sheets  and  other  places  which  might  harbor  ticks  should  be 
dusted  with  pyrethrum  insect  powder. 

The  nearly  allied  0.  savignyi  of  Abyssinia,  which  conceals  itself 
in  dusty  soil  to  a  depth  of  one  inch,  can  best  be  destroyed  in  in- 
fested camp  sites,  environs  of  wells,  etc.,  by  harrowing  the  sur- 
face of  the  ground,  strewing  dry  grass  and  brush  over  it,  and 
burning  it  from  around  the  edge  of  the  infested  area  toward  the 
center.  Spraying  with  antiseptics  has  been  found  practically 
useless,  since  even  the  total  immersion  of  ticks  in  strong  antisep- 
tics for  an  hour  or  more  fails  to  kill  them. 

The  fowl  tick  or  "  miana  bug,"  Argas  persicus,  and  the  Ameri- 
can hut-infesting  species  of  Ornithodorus,  0.  talaje  and  0.  turicata, 
can  be  controlled  by  methods  similar  to  those  used  for  the 
tampan. 


CHAPTER  XXII 

BEDBUGS   AND   THEIR  ALLIES 

The  Order  Hemiptera.  —  The  order  of  insects,  Hemiptera  (or 
Rhynchota),  which  includes  the  true  bugs,  contains  a  number 
of  species  which  habitually  or  occasionally  attack  man.  The 
most  important  of  these  are  the  bedbugs,  which  are  found  all 
over  the  world  in  temperate  and  tropical  climates.  There  are 
few  objects  which  are  more  disgusting  than  bedbugs  to  good 
housekeepers,  yet  there  are  few  who,  at  one  time  or  another, 
have  not  had  to  contend  with  them  or  at  least  guard  against 
them.  Belonging  to  an  allied  family  are  the  cone-noses,  larger 
than  bedbugs  and  not  devoid  of  wings,  fiercer  in  disposition  and 
capable  of  producing  much  more  painful  bites.     A  considerable 

number  of  species  of  these  bugs 

are  known  and  are  found  in  all 

warm  countries.    The  relation  of 

bugs  to  disease  is  still  very  im- 

FiG.  162.    A  hemipteran  wing         perfectly  known,  but  these  para- 

^  ^^"  sites    are    positively    known    to 

transmit  at  least  one  important  disease,  and  are  suspected  of 

transmitting  several  others. 

The  true  bugs,  order  Hemiptera,  are  characterized  by  having 
piercing  and  sucking  mouthparts  contained  in  a  jointed  beak 
and  by  an  incomplete  metamorphosis,  i.e.,  not  undergoing  a 
complete  transformation  from  a  larval  to  an  adult  form  during  a 
period  of  rest,  as  do  such  insects  as  butterflies,  beetles,  etc.  The 
newly  hatched  young  may  differ  quite  considerably  from  the 
adult,  but  the  mature  characteristics  are  gradually  attained  with 
each  successive  moult.  The  order  is  divided  into  two  suborders, 
only  one  of  which,  the  Heteroptera,  concerns  us  here.  In  the 
members  of  this  group  the  first  pair  of  wings,  if  present,  have  a 
thickened,  leathery  basal  portion  and  a  membranous  terminal 
portion  (Fig.  162).  The  second  pair  of  wings  are  always  mem- 
branous when  present. 

370 


STRUCTURE  OF   BEDBUGS 


371 


Bedbugs 

General  Account.  —  The  bedbugs  belong  to  the  family  Cimi- 
cidse.  They  have  broad  flat  bodies,  and  are  devoid  of  wings, 
except  for  a  pair  of  spiny  pads  which  represent  the  first  pair  of 
wings  (Fig.  163).  The  first  segment  of  the  thorax  has  winglike 
expansions  at  the  sides  which  grow  forward  and  partially  sur- 
round the  small  head.  In  the 
male  the  abdomen  is  quite 
pointed  at  the  tip,  whereas  in 
the  female  it  is  evenly  rounded, 
the  contour  of  the  abdomen 
being  almost  a  perfect  circle  in 
unfed  bugs.  The  eyes  project 
prominently  at  the  sides  of  the 
head,  the  flexible  four-jointed 
antennae  are  constantly  moved 
about  in  front  of  the  head, 
and  the  jointed  beak  is  folded 
under  the  head  so  that  it  is 
entirely  invisible  from  above. 
The  legs  have  the  usual  seg- 
ments, the  tarsi  being  three- 
jointed.  The  greater  part  of 
the  body  is  covered  with  bristles 
set  in  little  cup-shaped  depres- 
sions. These  depressions  are  perforated  at  the  bottom  to  allow 
for  the  passage  of  muscles  which  move  the  bristles.  Murray 
describes  having  seen  bugs  raise  the  bristles  upon  meeting  each 
other  as  cats  raise  their  hairs  or  birds  their  feathers.  The  bristles 
are  of  two  kinds,  one  a  simple  slender  spine,  the  other  with  a 
stouter  flattened  end,  with  sawlike  teeth  along  the  thinner  edge. 
In  addition  to  both  kinds  of  bristles,  the  legs  also  have  a  dense 
brush  of  hairs  at  the  end  of  each  tibia.  When  a  bug  is  distended 
with  blood  a  smooth  shining  band  can  be  seen  at  the  base  of  each 
abdominal  segment  where  no  bristles  occur  (Fig.  163).  These 
bands  are  the  portions  of  the  segments  which  are  not  ordinarily 
exposed,  being  overlapped  by  the  preceding  segment. 

One  of  the  most  striking  characteristics  of  bedbugs  is  the 
peculiar  pungent  odor  so  well  known  to  all  who  have  had  to  con- 


Fig.   163. 


Bedbug,  Cimex  lectularius, 
female.    X  10. 


372 


BEDBUGS  AND  THEIR  ALLIES 


tend  with  these  pests.  Many  other  bugs  are  characterized  by 
similar  odors,  as,  for  example,  the  common  "  stink-bugs."  The 
odor  is  produced  by  a  clear  volatile  fluid  secreted  by  a  pair  of 

glands  of  very  variable  size  which 
open  between  the  bases  of  the  hind 
pair  of  legs.  Although  in  most 
''wild"  bugs  the  stink  glands  are 
supposed  to  be  distinctly  bene- 
ficial in  that  they  make  the  owners 
obnoxious  to  enemies  which  would 
otherwise  prey  upon  them,  they 
are  a  decided  handicap  to  the  do- 
mestic bedbugs  in  the  struggle  for 
existence,    since   the   odor    draws 

F,G.  164.   Head  and  part  of  thorax  attention  to  the  presence  of  bugs 
of  bedbug,  ventral  view.   X  20.    Note  which    might    Otherwise     escape 

jointed  beak,  eyes  and  stout  spines.  ^^^:^^q  js^^r  doeS  the  SCent  ap- 
pear to  be  any  protection  to  them  against  such  enemies  as  cock- 
roaches and  red  ants.  Murray  suggests  that  it  may  be  of  some 
use  to  them  in  their  social  intercourse 
in  the  dark  recesses  in  which  they 
spend  their  lives. 

The  nasty  odor  of  bedbugs  has 
evidently  inspired  some  faith  in  their 
medicinal  value.  Seven  bugs  ground 
up  in  water  was  said  by  Pliny  to 
arouse  one  from  a  fainting  spell,  and 
one  a  day  would  render  hens  immune 
to  snake  bites.  Even  at  the  present 
time  there  are  places  in  civilized  coun- 
tries where  bedbugs  are  given  as  an 
antidote  for  fever  and  ague. 

There  are  a  number  of  species  of      _,     ,^^tj-     v.  ^u     ^■ 

f  IG.  165.    Indian  bedbug,  Cimex 
bugs   in   the   genus   CimeX,    but  some    hemij4erus(rotundatus),iemale.    X 

of  the  species  confine  their  attentions  «•     (^^^^^  Casteiiani  and  Chai- 

1         1  •     1      1  mers.) 

to  poultry  and  other  birds,  bats,  etc. 

There  are  two  widely  distributed  species  which  attack  man:  one 
is  the  common  bedbug,  Cimex  ledularius,  found  in  all  temperate 
climates;  the  other  is  the  tropical  or  Indian  bedbug,  Cimex  hemip- 
terus  {rotundatus) ,  prevalent  in  many  tropical  countries,  includ- 


HABITS  OF  BEDBUGS  373 

ing  southern  Asia,  Africa,  the  West  Indies  and  South  America. 
The  tropical  bug  (Fig.  165)  differs  from  the  common  one  only  in 
minor  details,  such  as  greater  length  of  body  hairs,  darker  color 
and  more  elongate  abdomen.  It  is  less  dependent  on  human 
blood  than  its  relative  of  temperate  climates,  and  readily  attacks 
not  only  rats  and  mice  but  also  bats  and  birds.  Both  species  are 
reddish  brown  in  color,  becoming  deep  red  when  gorged  with 
blood.     Another  species,  C.  boueti,  attacks  man  in  Guiana. 

Habits.  —  Bedbugs  are  normally  night  prowlers,  and  exhibit 
a  considerable  degree  of  cleverness  in  hiding  away  in  cracks  and 
crevices  during  the  daytime.  When  hungry  they  will  frequently 
come  forth  in  a  lighted  room  at  night,  and  have  even  been  known 
to  feed  in  broad  daylight.  Favorite  hiding  places  are  in  old- 
fashioned  wooden  bedsteads,  in  the  crevices  between  boards, 
under  wall  paper,  and  other  similar  places,  for  which  their  fiat 
bodies  are  eminently  adapted.  Like  other  animals  which  have 
long  associated  with  man,  bedbugs  have  developed  much  cun- 
ning in  their  ability  to  adapt  themselves  to  his  habits.  Marlatt 
says  "  the  inherited  experience  of  many  centuries  of  companion- 
ship with  man,  during  which  the  bedbug  has  always  found  its 
host  an  active  enemy,  has  resulted  in  a  knowledge  of  the  habits 
of  the  human  animal  and  a  facility  of  concealment,  particularly 
as  evidenced  by  its  abandoning  beds  and  often  going  to  distant 
quarters  for  protection  and  hiding  during  daylight,  which  in- 
dicate considerable  apparent  intelligence."  Their  ability  to 
gain  access  to  sleepers  at  night  is  hardly  less  remarkable.  Cases 
are  reported  of  bedbugs  creeping  along  ceilings  and  dropping  down 
on  beds  in  order  to  reach  their  hosts,  but  these  may  have  been 
accidental. 

The  bedbug  makes  himself  a  great  pest  wherever  he  occurs 
by  the  unsparing  use  of  his  piercing  and  sucking  mouthparts. 
The  latter  consist  of  four  needle-like  organg  lying  in  the  long, 
jointed  lower  lip  or  beak,  a  pair  of  flattened  sharp-pointed  man- 
dibles and  a  pair  of  slightly  shorter  maxillae  with  serrated  edges. 
The  beak  is  grooved  in  such  a  way  that  the  sides  of  the  groove 
almost  close  together,  thus  forming  a  protective  sheath  for  the 
stilettos  inside.  When  about  to  indulge  in  a  meal  the  beak  is 
bent  back,  and  the  piercing  organs,  gliding  up  and  down  past 
each  other,  are  sunk  into  the  flesh  of  the  victim  (Fig.  166).  A 
strong  sucking  motion  of  the  .pharynx,  into  which  a  bit  of  sali- 


374  BEDBUGS  AND  THEIR  ALLIES 

vary  juice  has  already  been  poured,  draws  blood  up  through  a 
tube  made  by  the  piercing  organs,  through  a  thickened  ''  bottle 
neck  "  ring  to  the  oesophagus  and  then  into  the  relatively  enor- 
mous stomach.  The  muscles  for  dilating  the  pharynx  in  order 
to  make  a  suction  pump  out  of  it  occupy  the  greater  part  of  the 
head.  According  to  Cragg,  who  has  worked 
on  the  alimentary  tract  and  digestive  proc- 
ess of  bedbugs,  there  are  about  70  pulsa- 
^^  tions  of  the  pharynx  per  minute  in  young 
bugs,  in  which  this  can  be  observed  through 

Fig.  166.  Diagram  the  body  wall.  Bugs  Seldom  cling  to  the 
SrNotTJ^iilot  «ki°  while  sucking,  preferring  to  remain 
of  proboscis.      (After  on  the  clothing.     Since  a  fresh  meal  appar- 

"^^^^"-^  ently  acts  as  a  stimulus  for  emptying  the 

contents  of  the  rectum,  the  adherence  to  the  clothing  is  a  fortunate 
circumstance,  inasmuch  as  it  precludes  to  some  extent  the  danger 
of  bedbugs  infecting  their  wounds  with  excrement,  as  do  ticks. 

In  the  course  of  ten  or  15  minutes  a  full  meal  is  obtained  and 
the  bug,  no  longer  flat  but  round  and  distended  with  blood,  re- 
treats to  his  hiding  place,  having  first  deposited  a  bit  of  excrement. 
According  to  Cragg,  in  the  case  of  C  hemipterus  (rotundatus) ,  a 
single  meal,  much  of  which  is  temporarily  stored  in  the  stomach 
which  acts  as  a  food  reservoir  as  well  as  a  digestive  organ,  is  not 
fully  assimilated  for  at  least  a  week,  although  the  bug  is  ready  to 
feed  again  in  a  day  or  two,  thus  having  parts  of  several  meals  in 
the  stomach  at  once.  This  is  quite  a  different  condition  from 
that  found  in  most  blood-sucking  insects,  where  a  meal  is  com- 
pletely digested  before  another  is  sought.  Observations  made 
by  several  authors  on  C.  ledularius  do  not  indicate  that  this 
species  has  similar  habits.  As  in  other  bugs,  the  digestive  juices 
change  the  absorbed  blood  into  a  dense  black  mass,  described 
by  Murray  as  almost  like  lamp-black. 

The  bite  of  the  bedbug  seldom  produces  pain  or  swelling  unless 
rubbed  or  scratched,  a  fact  which  indicates  either  that  the  saliva 
is  not  irritating  or  that  it  does  not  ordinarily  reach  the  wound 
before  sucking  begins.  In  some  people,  however,  a  stinging,  hard, 
white  swelling  is  produced. 

Under  normal  conditions  the  common  bedbug,  C.  ledularius, 
has  only  rarely  been  found  feeding  on  anything  but  human  blood. 
The  bugs  which  infest  the  nests  of  swallows  and  other  birds  are 


LIFE  HISTORY  OF  BEDBUGS  375 

of  different  species  from  the  human  pests,  and  are  not  known  to 
annoy  man  voluntarily,  although  they  occasionally  enter  rooms 
from  the  nests  of  chimney  swifts.  Bats  are  often  accused  of 
carrying  bedbugs  into  houses,  but  they,  too,  are  attended  by 
their  own  particular  species  which  does  not  attack  man.  The 
assertion  that  bedbugs  can  be  found  under  bark  and  moss  out 
of  doors  also  arises  from  a  misapprehension.  These  bugs  are 
really  the  immature  stages  of  certain  other  species  of  bugs  which 
resemble  bedbugs  closely  enough  to  be  mistaken  for  them  by  a 
casual  observer. 

Although  human  blood  is  their  normal  food,  bedbugs  are  able 
to  subsist  on  the  blood  of  such  animals  as  rats,  mice,  rabbits, 
cats,  dogs  and  even  chickens.  It  has  also  been  shown  that  bugs 
will  suck  blood  from  freshly  killed  mice.  By  utilizing  mice 
and  rats  as  a  food  supply  they  are  able  to  exist  in  deserted  build- 
ings for  a  long  time.  Furthermore  they  are  able  to  endure  long 
fasts;  they  have  been  kept  alive  without  any  food  whatever  for 
a  year.  Murray  has  found  that  bugs  which  have  been  starved 
even  for  a  long  time  pass  unaltered  blood  corpuscles  in  their 
faeces,  and  suggests  that  a  small  quantity  of  food  may  be  re- 
tained undigested  in  the  rectum  to  be  drawn  upon  very  slowly  in 
time  of  need,  though  when  a  fresh  supply  of  blood  is  obtained 
the  old  store  is  cleared  out.  Bugs  also  store  up  a  great  deal  of 
fat  for  use  in  time  of  famine.  Sometimes,  however,  after  a  house 
has  been  deserted  for  some  time,  and  their  normal  supply  of 
food  is  cut  off,  the  bugs  migrate  in  search  of  an  inhabited  house. 
In  cold  weather  bugs  hibernate  in  a  semi-torpid  condition  and 
do  not  feed,  but  in  warm  climates  they  are  active  the  year  around. 
The  common  bedbug,  according  to  Marlatt,  is  sensitive  to 
temperatures  of  96°  F.  to  100°  F.  or  more  if  accompanied  by  a 
high  degree  of  humidity,  and  is  killed  in  large  numbers  under  such 
climatic  conditions.  According  to  Bacot,  unfed  newly  hatched 
bugs  are  able  to  withstand  cold  between  28°  F.  and  32°  F.  for 
as  much  as  18  days,  though  they  are  destroyed  by  exposure  to 
damp  cold  after  a  full  meal. 

Life  History.  —  The  eggs  of  bedbugs  (Fig.  167 A)  are  pearly 
white  oval  objects,  furnished  with  a  little  cap  at  one  end  which 
is  bent  to  one  side.  As  in  the  case  of  lice,  the  eggs  are  relatively 
large,  being  about  one  mm.  (^V  of  an  inch)  in  length,  and  are 
therefore  laid  singly  or  in  small  batches.     The  ovaries  hold  about 


376  BEDBUGS  AND  THEIR  ALLIES 

40  eggs  at  a  time,  all  near  the  same  stage  of  development,  so 
they  must  undergo  rapid  increase  in  size  shortly  before  being 
deposited.  Girault,  who  has  carried  out  extensive  breeding 
experiments,  saw  one  female  lay  111  eggs  during  the  61  days 
that  he  had  her  in  captivity,  and  another  laid  a  total  of  190 
eggs.  Often  a  female  returns  to  lay  more  eggs  in  the  same 
place  so  that  batches  of  40  or  more  can  be  found  in  the  crevices 
where  the  adult  insects  hide. 

The  eggs  hatch  in  from  six  to  ten  days  during  warm  weather, 
but  are  retarded  in  their  development  by  cold.     A  week  of 

freezing  temperature  reduces  the 
hatching  to  25  per  cent.  The 
freshly  hatched  bugs  (Fig.  167B) 
are  very  small,  delicate  and  pale 
in  color.  After  their  first  hearty 
meal  they  have  a  much  more 
robust  appearance,  and  grow 
rapidly.  The  skin  is  normally 
moulted  five  times  before  the  final 
Fig.  167.     Egg  and  newly  hatched  adult  stage  is  reached,  at  least 

larva  of  bedbug.      X  20.     (After  Mar-  ,    ,  .  r      j  t_    • 

1^1-^ )  one  gluttonous  teed  bemg  neces- 

sary before  each  moult  in  order 
to  insure  normal  development  and  reproduction.  Although 
apparently  not  necessary  to  its  development,  the  bug  may  gorge 
itself  several  times  between  moults,  at  intervals  of  about  one  to 
six  days.  Marlatt  found  the  average  period  of  time  between 
moults  to  be  eight  days.  Allowing  a  similar  length  of  time 
for  the  hatching  of  the  eggs,  the  time  occupied  from  laying  of 
the  eggs  to  maturity  is  about  seven  weeks.  Girault  has  found 
the  development  from  the  hatching  of  the  eggs  to  maturity  to 
take  place  in  as  short  a  time  as  29  days.  On  the  other  hand, 
starvation,  cool  temperatures  and  possibly  other  conditions  may 
drag  out  the  period  of  development  to  great  length.  Bacot 
found  that  the  newly  hatched  larvae  could  live  unfed  four  and  a 
half  months  and  with  one  feed  for  nine  months.  The  several 
larval  stages  of  the  insect  resemble  each  other  quite  closely  except 
in  the  constantly  increasing  size  and  deepening  color.  The 
wing  pads  appear  only  after  the  last  moult. 

Bedbugs  and  Disease.  —  The  relation  of  bedbugs  to  human 
disease  is  a  subject  which,  although  a  problem  of  the  most  vital 


BEDBUG  AS  DISEASE  CARRIER  377 

interest  in  preventive  medicine,  is  still  very  indefinitely  known. 
Various  authors  have  associated  bedbugs  with  a  number  of 
human  diseases  but  the  evidence  brought  forth  in  support  of 
these  insects  being  the  normal  transmitters  of  the  diseases  in 
question  rests  on  insecure  foundations.  Ordinarily  bugs  are 
handicapped  in  the  extent  to  which  they  are  able  to  spread 
disease  by  their  non-migratory  habits.  Unlike  many  parasites 
they  are  not  usually  carried  about  by  human  beings,  but  remain 
permanently  in  places  occupied  by  their  hosts.  It  is  obvious, 
therefore,  that  bugs  are  limited  in  the  spreading  of  disease  to  the 
occupants  of  the  infested  place.  Should  this  be  a  private  home, 
spread  of  disease  by  bugs  would  be  practically  limited  to  a  single 
family.  In  case  of  infested  hotels,  rooming  houses,  sleeping 
cars,  boats,  etc.,  conditions  are  ideal  for  the  spread  of  disease  by 
bugs,  and  it  can  hardly  be  doubted  that  it  is  in  such  places  that 
most  of  the  damage  is  done. 

One  of  the  first  accusations  against  the  bedbug  as  a  disease 
carrier  was  made  by  Patton,  of  the  British  Medical  Service  in 
India,  who  in  1907  brought  evidence  against  this  insect  as  a 
carrier  of  Indian  kala-azar  (see  p.  79).  Patton  followed  what 
he  believed  to  be  developmental  stages  of  the  parasite  of  kala- 
azar,  a  species  of  Leishmania,  in  the  gut  of  the  Indian  bedbug, 
Cimex  hemipterus  (rotundatus) .  Subsequent  investigations,  es- 
pecially recent  ones  by  Cornwall,  have  shown  that  infection  of 
bedbugs  by  feeding  on  kala-azar  patients  is  very  rare,  and  that 
the  bugs  cannot,  apparently,  transmit  the  infection  either  by 
biting  or  by  means  of  infected  faeces.  The  rare  infectivity  of 
bugs  which  have  fed  on  kala-azar  patients,  however,  may  be 
correlated  with  the  fact  that  the  kala-azar  parasites  are  rare  in 
the  peripheral  blood.  As  pointed  out  by  Price  and  Rogers, 
even  if  only  a  small  per  cent  of  bugs  become  infective,  where 
they  are  as  numerous  as  they  are  in  this  coolie  huts  in  India, 
they  would  be  able  to  spread  the  disease  successfully.  Donovan 
believes  the  kala-azar  parasites  may  utilize  the  Malay  bug,  Tri- 
atoma  rubrofasciatus  (see  p.  381),  as  an  intermediate  host,  but 
retTent  work  is  tending  to  throw  doubt  on  the  necessary  in- 
strumentality of  any  insect  in  transmitting  the  disease.  Bed- 
bugs have  also  been  associated  with  another  Leishmania  disease, 
oriental  sore,  but  it  is  doubtful  whether  the  bugs  act  as  more 
than  mechanical  disseminators  of  the  parasite,  if  at  all.     Yaki- 


378  BEDBUGS  AND  THEIR  ALLIES 

moff  in  Turkestan  and  Cornwall  in  India  were  unable  to  infect 
bedbugs  with  parasites  of  oriental  sore  even  when  the  bugs  were 
fed  directly  on  the  ulcers.  On  the  other  hand,  the  fact  that  one 
species  of  Cimex,  C.  pipistrelli,  transmits  a  trypanosome  disease 
of  bats  would  lead  one  to  suspect  their  ability  to  transmit  a 
Leishmanian  disease,  since  the  two  groups  of  parasites  are 
certainly  near  relatives.  Several  workers  have  incriminated 
bedbugs  as  carriers  of  European  relapsing  fever,  especially  in 
Serbia  and  in  the  southeastern  part  of  Europe,  but  there  can  be 
little  doubt  but  that  lice  are  the  normal  transmitters  of  the 
European  as  well  as  the  North  African  form  of  relapsing  fever. 
In  Moscow,  for  instance,  Bayon  found  that  relapsing  fever  was 
practically  unknown  among  the  better  class  of  people  who  were 
personally  clean,  even  though  living  in  bug-infested  quarters, 
whereas  the  fever  was  very  prevalent  among  the  lower  classes, 
most  of  whom  were  lousy,  even  though  they  were  kept  in  hos- 
pitals where  no  bugs  existed.  On  the  other  hand,  Hagler,  who 
worked  with  the  American  Red  Cross  expedition  in  Serbia  in 
1915,  points  out  that  while  typhus  disappeared  with  the  exter- 
mination of  lice,  relapsing  fever  continued  to  develop  in  the 
Belgrade  hospital  until  the  latter  was  fumigated  for  bedbugs. 
The  Indian  bedbug,  C.  hemipterus,  is  believed  by  some  workers 
to  be  a  common  transmitter  of  Indian  relapsing  fever,  though 
evidence  points  strongly  to  the  instrumentality  or  lice  and  ticks 
in  spreading  the  disease.  Spirochceta  carteri,  the  organism  of 
Indian  relapsing  fever,  has  been  observed  to  remain  alive  for 
from  four  to  seven  days  in  the  alimentary  canal  of  bugs  which 
have  fed  on  infected  monkeys,  but  bugs  seldom  become  infected 
from  human  cases. 

As  remarked  elsewhere,  bedbugs  have  been  found  capable  of 
acting  as  intermediate  hosts  for  the  trypanosome,  T.  cruzi,  of 
Chagas'  disease,  but  they  usually  remain  infective  for  a  much 
shorter  time  than  do  bugs  of  the  genus  Triatoma.  Bedbugs  have 
been  found  capable  of  transmitting  the  infection  to  guinea-pigs 
in  from  21  hours  to  77  days  after  an  infective  feed. 

That  bedbugs  may  act  as  mechanical  spreaders  of  various 
diseases  is  unquestionable.  Experiments  show  that  the  bacilli 
of  bubonic  plague  can  develop  in  the  gut  of  bugs,  though  more 
slowly  than  in  fleas,  and  with  a  much  higher  mortality  for  the 
bugs.     That  they  may  act  as  transmitters  of  the  disease  is  quite 


TRIATOMA  379 

certain,  and  bugs  have  been  found  to  remain  infective  for  48 
days  if  they  did  not  early  succumb  to  the  disease.  Leprosy  also 
can  probably  be  spread  by  bugs  in  a  mechanical  manner,  and  it 
is  reasonable  to  believe  that  such  diseases  as  tuberculosis  and 
syphilis  may  likewise  be  carried  by  them. 

Other   Parasitic  Bugs 

Most  of  the  other  true  bugs  which  may  be  looked  upon  as 
normally  human  parasites  belong  to  the  family  Reduviidse.  This 
is  a  large  family  of  rapacious  bugs,  many  of  them  bright  colored, 
which  are  especially  numerous  in  the  tropics.  Most  of  them 
prey  upon  other  insects,  but  nearly  all  of  them  produce  painful 
wounds  when  they  bite  man.  Nearly  all  are  active  runners  and 
good  fliers. 

Triatoma,  —  By  far  the  most  important  species  are  the  mem- 
bers of  the  genus  Triatoma  (Conorhinus),  popularly  known  as 
cone-noses,  "  big "  bedbugs  and  by  numerous  local  names. 
There  are  about  40  species,  most  of  them  in  South  and  Central 
America.  T.  sanguisuga  of  southern  United  States  is  the  well- 
known  ''  Mexican  bedbug."  It  is  a  bug  about  one  inch  in  length 
with  a  flat,  dark  brown  body,  the  edges  of  which,  not  covered  by 
the  wings,  are  marked  with  pinkish  bars.  The  long  conical  head 
is  furnished  with  a  strong  beak.  Its  bite,  like  that  of  others  of 
the  family,  is  very  painful  and  causes  swelling,  sometimes  fol- 
lowed by  effects  which  may  last  a  year. 

The  salivary  secretion  is  evidently  very  poisonous  and  not 
unlike  snake  venom  in  the  extensive  swelling  and  irritation  which 
it  causes.  The  adult  bugs  attack  not  only  man  but  other  mam- 
mals also,  while  the  nymphs  often  annoy  chickens.  Unhke  the 
bedbug  this  insect  can  fly,  and  will  readily  enter  rooms  at  night 
to  attack  sleepers  unless  screened  out.  The  eggs  are  white, 
oval  objects  when  first  laid,  soon  turning  yellowish  and  then 
brownish;  they  are  laid  in  small  batches  under  logs  or  stones 
outdoors.  They  hatch  in  about  20  days  into  young  bugs  which 
probably  prey  very  largely  on  other  insects.  After  four  moults 
the  insect  reaches  the  adult  winged  condition  in  which  it  is 
most  troublesome  as  an  invader  of  houses.  This  species  is  re- 
placed by  T.  protracta  in  southwestern  United  States. 

The  most  important  species  of  the  genus  are  those  which  are 


380 


BEDBUGS  AND  THEIR  ALLIES 


naturally  infected  with  Trypanosoma  cruzi  in  South  America. 
On  account  of  its  domestic  habits,  Triatoma  megista  (Fig.  168) 
is  the  most  important  species  in  the  transmission  of  the  disease 
to  man.  This  bug  is  a  large,  handsome,  black  and  red  insect, 
locally  known  as  the  "  barbeiro,"  which  infests  the  dirty  thatched 
houses  of  the  natives  in  the  state  of  Minas  Geraes  in  Brazil. 
It  is  nocturnal  in  habit,  coming  forth  from  its  hiding  places  in 
the  thatch  of  the  roof  or  in  the  debris  of  the  floor  to  feed  upon 

its  human  victims  after  the  man- 
ner of  bedbugs.  The  bugs  are 
so  active  and  hide  so  rapidly 
when  a  light  is  produced  during 
their  foraging  in  the  dark  that, 
they  can  seldom  be  caught.  The 
details  of  the  development  of  the 
trypanosome  of  Chagas'  disease 
in  this  insect  and  the  relation 
of  the  insect  to  the  disease  are 
described  in  Chapter  VI,  p.  110. 
Torres  beheves  the  bugs  almost 
invariably  become  infected  by 
feeding  on  infected  vertebrates, 
since  Triatoma  does  not  devour 
excrement  of  its  own  species, 
as  does  the  allied  Rhodnius  pro- 
lixus,  and  cannibalism  is  rare 
among  these  bugs,  except  in  young 
larvse  which  sometimes  feed  on 
each  other. 

The  life  history  of  the  barbeiro  is  quite  hke  that  of  other 
members  of  the  genus,  except  that  the  eggs  are  laid  in  or  about 
human  habitations.  The  eggs  hatch  in  from  20  to  40  days  and 
the  young  pass  through  five  moults  to  reach  maturity,  the  whole 
life  cycle  occupying  about  a  year.  The  females  begin  depositing 
eggs  about  a  month  after  the  last  moult.  These  insects  suck 
blood  at  intervals  of  from  four  days  to  several  months. 

A  number  of  other  South  and  Central  American  species  of 
Triatoma  have  been  found  to  harbor  Trypanosoma  cruzi  or  a 
species  indistinguishable  from  it.  Triatoma  geniculata,  which 
inhabits  the  burrows  of  the  armadillo  and  various  rodents,  is 


Fig.    168.      The    "barbeiro,"     Tria- 
toma megista.    X  l^.     (After  Chagas.) 


TRIATOMA  381 

known  to  infect  these  animals  in  nature,  and  the  armadillo  is 
possibly  an  important  reservoir  of  the  disease.  Triatoma  chagasi 
which  had  fed  on  a  rodent  known  as  the  '*  moco,"  Cerodon 
rupestris,  in  an  uninhabited  desert  region  was  found  to  be  infected. 
T.  vitticeps,  occurring  near  Rio  de  Janeiro,  T.  sordida  of  Sao 
Paulo  and  T.  dimidiata  of  San  Salvador  in  Central  America 
have  been  found  infected  with  trypanosomes  thought  to  be  iden- 
tical with  the  species  causing  Chagas'  disease,  and  these  species 
have  been  shown  to  be  capable  of  transmitting  the  infection  to 
guinea-pigs.  In  Argentina,  as  well  as  throughout  most  of 
Brazil,  T.  infestans,  the  vinchuca  or  "  great  black  bug  of  the 
Pampas,"  described  by  Darwin  in  his  "  Voyage  of  a  Naturalist  " 
as  a  vicious  human  pest,  has  been  found  to  harbor  a  similar 
trypanosome,  but  whether  or  not  Chagas'  disease  exists  in 
Argentina  is  still  in  doubt.  T.  protrada  of  southwestern  United 
States  has  been  shown  recently  by  Kofoid  and  McCulloch  to 
harbor  a  trypanosome  which  exhibits  only  slight  differences  from 
Trypanosoma  cruzi,  and,  as  intimated  by  the  discoverers,  may 
possibly  be  merely  a  variety  of  the  same  species  though  named 
by  them  T.  triatomce.  The  widely  distributed  T.  rubrofasciata 
was  shown  by  Neiva  to  become  infected  with  trypanosomes  after 
feeding  on  an  infected  guinea  pig.  From  all  this  evidence,  and 
from  the  fact  that  other  species  of  bugs  of  different  genera  and 
families,  including  the  bedbugs,  are  experimentally  susceptible 
to  the  infection  and  capable  of  transmitting  it  to  rodents,  it  is 
possible  that  all  the  species  of  Triatoma  and  alUed  genera  in  South 
and  Central  America  may  be  potential  transmitters  of  the  in- 
fection. CannibaHsm  is  common  among  many  of  these  bugs, 
and  may  make  possible  a  direct  spreading  of  trypanosome  in- 
fection from  bug  to  bug. 

The  *'  Malay  bug,"  T.  rubrofasciata,  of  tropical  Asia  and  some 
parts  of  Africa  and  Madagascar  is  a  closely  allied  species.  With 
its  huge  proboscis  it  produces  a  nasty  sting  which  is  followed  in 
a  few  minutes  by  acute  pain  and  swelling.  Although  it  feeds  on 
man  by  preference,  it  attacks  a  number  of  other  mammals  and 
even  insects.  Large  nymphs  or  adults,  which  are  an  inch  or 
more  in  length,  are  said  to  consume  about  one  cc.  of  blood  at 
a  meal,  and  they  feed  at  intervals  of  from  three  to  six  days.  The 
breeding  habits  are  similar  to  those  of  other  cone-noses.  In 
the  islands  of  Mauritius  and  Reunion  the  stomach  and  intestines 


382  BEDBUGS  AND  THEIR  ALLIES 

of  this  bug  have  been  found  to  contain  trypanosomes  in  all 
phases  of  development,  and  of  very  variable  form,  possibly 
representing  several  species.  These  trypanosomes  can  be 
inoculated  into  mice  and  rats  and  it  is  suggested  that  under 
certain  conditions  they  or  others  living  in  the  gut  of  the  bug  may 
cause  disease  in  man.  A  number  of  cases  are  on  record  where 
irregular  fevers  have  followed  the  bites  of  this  insect.  Since  these 
fevers  were  shown  to  be  non-malarial  and  showed  symptoms  of 
typical  trypanosome  infection,  it  is  possible  that  such  an  infec- 
tion may  really  be  transmitted  to  man  by  this  bug  as  well  as 
by  its  close  relatives  in  South  America.  It  is  also  possible  that 
the  bug  may  serve  as  an  intermediate  host  for  the  kala-azar 
parasite. 

Other  Species.  —  Several  other  species  of  bugs  of  this  family 
occur  in  Africa.  One,  Acanthaspis  sulcipes,  has  been  thought 
to  be  the  possible  transmitter  of  a  form  of  endemic  goitre  in 
tropical  Africa.  In  North  America  the  family  is  further  repre- 
sented by  the  "  kissing  bugs,"  of  the  genus  Melanolestes.  The 
common  kissing  bug  or  "  black  corsair,"  M.  picipes,  became  very 
abundant  in  the  United  States  a  few  years  ago  and  gave  op- 
portunity for  many  startling  newspaper  stories.  It  is  a  large 
black  bug  with  reddish  marks  on  the  back  and  legs.  Its  bite 
much  resembles  that  of  a  wasp,  though  often  much  more  serious, 
occasioning  more  than  local  symptoms  and  even  vomiting. 
Allied  bugs  of  the  genera  Reduvius,  Rasahus 
and  Melanolestes  occur  in  the  warm  parts  of 
North  and  Central  America,  and  frequently 
attack  man  and  other  mammals,  though 
their  normal  food  in  most  cases  is  insects. 

In  Venezuela  and  other  parts  of  northern 
South  America  a  very  common  bug  which  in- 
fests houses  is  Rhodnius  prolixus,  a  species 
which  has  been  found  capable  of  transmitting 
Fig.  169.  Pito  bug,  Trypanosoma  cruzi.  This  species  is  not  only 
(A^ter  Akock.)  ^^^  ^^  cannibalistic  in  habits,  but  also  devours  excre- 
ment of  other  bugs,  thus  suggesting  the  possi- 
bility of  direct  dissemination  of  trypanosomes  from  bug  to  bug. 
Of  other  families,  there  are  many  bugs  which  occasionally  attack 
man  but  few  which  commonly  do  so.  One  which  is  worthy  of 
mention  is  the  malodorous  pito  bug,  Dysodius  lunatus  (Fig.  169), 


FUMIGATION  383 

of  South  America,  belonging  to  the  family  Aradidse.     It  is  a 
large  broad  bug  which  frequents  houses  and  bites  severely. 

All  the  species  of  bugs  which  infest  houses  may  be  destroyed 
by  the  fumigation  methods  described  below,  but  all  but  the  bed- 
bugs must  be  kept  out  by  screening,  since  they  are  not  handi- 
capped in  their  migrations  by  degeneration  of  the  wings. 


Remedies  and   Prevention 

Prevention  of  "  bugginess,"  at  least  in  the  case  of  bedbugs, 
consists  chiefly  in  good  housekeeping,  but  occasional  temporary 
infestations  are  likely  to  occur  in  almost  any  inhabited  building. 
A  number  of  remedies  for  bugs  have  been  advocated,  of  which 
the  best  is  undoubtedly  fumigation  with  hydrocyanic  acid  gas, 
as  described  below.  Sulphur  is  also  valuable  for  fumigation  but 
is  not  so  harmless  to  household  goods  as  is  hydrocyanic  acid  gas. 
When  the  infested  parts  of  houses  or  rooms  can  be  easily  located, 
good  remedies  are  kerosene,  gasolene,  turpentine  or  other  coal-tar 
products  painted  into  all  the  infested  cracks  and  crevices,  es- 
pecially in  the  woodwork  of  beds.  An  effective  remedy  of  this 
nature  is  a  mixture  of  one  ounce  corrosive  sublimate,  two  cups 
alcohol,  one-half  cup  turpentine.  These  substances  should  be 
applied  several  times  at  intervals  of  a  week  in  order  to  destroy 
newly  hatched  bugs.  Some  housekeepers  take  infested  beds 
apart  and  pour  boiling  water  into  the  "  buggy  "  parts,  thus 
effectually  killing  both  bugs  and  eggs  in  the  bed  but  this  does 
nothing  against  bugs  which  may  hide  elsewhere  than  in  the  bed. 
Bedbugs  have  a  number  of  natural  enemies,  among  which  may 
be  mentioned  especially  cockroaches,  red  ants  and  large  preda- 
ceous  bugs,  but  all  of  these  are  pests  themselves,  and  are,  there- 
fore, hardly  to  be  encouraged  as  bedbug  hunters,  efficient  as  they 
might  be  in  this  capacity. 


Fumigation 

Hydrocyanic  Acid  Gas.  —  Of  the  remedies  for  bugs  mentioned 
above,  fumigation  with  hydrocyanic  acid  gas  is  the  most  effective. 
This  gas  can  be  used  with  good  success  for  fumigation  of  houses, 
mills,  granaries,  greenhouses  or  any  other  closed  structure, 
against  any  kind  of  insect  pest.     But  since  the  gas  is  extremely 


384  BEDBUGS  AND  THEIR  ALLIES 

poisonous  not  only  to  insects  but  also  to  other  animals  and  to  man, 
its  use  must  be  accompanied  by  great  care  and  precaution.  A 
few  deep  breaths  of  the  gas  is  sufficient  to  cause  asphyxiation. 
On  the  other  hand  it  has  great  advantages  in  that  it  is  not  in- 
flammable or  explosive,  and,  unlike  sulphuric  fumes,  does  no 
damage  to  dry  foods  or  to  household  goods,  except  to  tarnish 
nickel  slightly.  Wet  foods  may  absorb  some  of  the  gas  and 
should  be  removed  before  fumigation.  Care  should  also  be 
taken  that  there  is  no  possible  avenue  of  escape  for  the  gas  into 
adjoining  rooms  or  houses  which  are  occupied.  The  character- 
istic peach-kernel  odor,  however,  makes  its  detection  easy,  thus 
removing  danger  of  asphyxiation  without  warning. 

The  gas  is  generated  by  the  action  of  sulphuric  acid  on  potas- 
sium cyanide.  The  procedure  as  advised  by  Herrick  is  as  fol- 
lows: Estimate  the  number  of  cubic  feet  in  the  room  or  house 
to  be  fumigated,  and  allow  one  ounce  of  potassium  cyanide  to 
every  100  cubic  feet.  Make  the  room  or  house  as  near  air  tight 
as  possible,  stopping  all  the  large  openings  such  as  fireplaces  and 
chimney  flues  with  old  rags  or  blankets.  Seal  cracks  about  win- 
dows and  doors  with  strips  of  wet  newspaper.  Such  strips  when 
thoroughly  wet  can  be  applied  quickly  and  effectively  over  cracks 
and  will  stick  tightly  for  several  hours,  and  can  be  removed  easily 
after  the  operation.  While  the  room  is  being  made  tight  some- 
one should  measure  out  the  required  ingredients  for  fumigation, 
allowing  one  fluid  ounce  of  crude  sulphuric  acid  and  three  fluid 
ounces  of  water  to  each  ounce  of  potassium  cyanide.  The  water 
first  should  be  poured  into  a  stone  crock  holding  two  gallons  or 
more,  i.e.,  large  enough  so  that  the  reacting  fluid  will  not  spatter 
on  floors  or  carpets.  The  crock  had  best  be  placed  on  several 
thicknesses  of  newspaper  or  on  an  old  rug  or  burlap  sack.  The 
required  amount  of  sulphuric  acid  should  then  be  poured  slowly 
into  the  water.  Never  pour  the  water  into  the  acid.  The  cyan- 
ide should  be  weighed  out  and  put  into  a  paper  bag  beside  the 
jar.  All  articles  which  might  suffer  from  the  gas  or  which  will 
be  needed  before  the  operation  is  over  should  be  removed  from 
the  room.  When  everything  is  ready  the  operator,  holding  his 
breath,  should  drop  the  paper  bag  of  cyanide  gently  into  the 
acid  jar,  and  walk  out  shutting  the  door  behind  him.  The  time 
required  for  the  acid  to  eat  through  the  paper  bag  in  order  to 
reach  the  cyanide  gives  ample  time  to  leave  the  room  before  the 


HYDROCYANIC  ACID  FUMIGATION 


385 


steamlike  gas  arises.  If  preferred,  however,  the  paper  bag  may 
be  suspended  by  a  string  passing  through  a  screw  eye  in  the 
ceiUng  and  through  the  key  hole  of  the  door  (Fig.  170).  The 
operator  may  then  lower  the  bag  into  the  jar  after  leaving  the 
room.  When  stringing  a  room  in  this  manner,  care  should  be 
taken  not  to  place  the  acid  jar  under  the  bag  until  everything  is 
ready.  The  fumigation  should  extend  over  a  period  of  five  or 
six  hours  at  least,  a  good  method  being  to  start  the  operation 
toward  evening  and  let  it  run 
all  night.  Better  results  will 
be  obtained  at  a  temperature 
of  70°  F.  or  above,  than  at 
a  lower  temperature. 

Two  or  three  hours  after 
the  doors  and  windows  have 
been  opened  the  gas  will  have 
disappeared  sufficiently  to 
allow  safe  entrance  into  the 

,1           u    -J.      T_       ij         2.  Fig.   170.     A  room   "strung"   for  hydro- 

room,    though   it    should   not  ^y^nic    acid    gas    fumigation    from    outside. 

be    occupied   until   the   char-  The  bag  of  cyanide  can  be  lowered  into  the 

....        J        •                     rnv  crock  of  sulphuric  acid  and  water  by  means 

acteristlC  odor  is  gone.      The  ^f  the  string.     (After  Herrick.) 

contents   of   the    generating 

jar  should  be  dumped  in  some  safe  place  and  the  jar  washed 
before  being  used  again.  When  a  whole  house  is  to  be  fumigated 
each  room  should  be  made  ready  as  described  above  and  then 
set  off  in  regular  order  beginning  on  the  upper  floor  and  working 
downward,  since  the  gas  is  lighter  than  air  and  therefore  rises. 
Herrick  describes  clearly  and  in  detail  the  method  which  he 
has  successfully  used  in  the  fumigation  of  large  dormitories. 
For  this  account  the  reader  is  referred  to  Herrick's  "  Insects 
Injurious  to  the  Household,"  pages  448  to  452. 

The  effectiveness  of  this  method  of  fumigation  against  bedbugs 
was  proven  by  experiments  conducted  by  Herrick.  Bugs  were 
placed  in  perforated  pill  boxes  and  wrapped  in  various  manners, 
some  with  three  inches  of  excelsior,  some  in  two  folds  of  a  thick 
comforter,  some  in  two  inches  of  cotton  batting  and  others  in  two 
folds  of  a  woolen  blanket.  Others  were  placed  in  a  cork  stop- 
pered vial,  the  cork  of  which  was  punched  twice  with  a  pair  of 
curved  forceps.  In  each  box  several  newly  laid  eggs  were  en- 
closed to  determine  the  effect  of  the  gas  on  their  hatching.     In 


386  BEDBUGS  AND  THEIR  ALLIES 

every  case  every  bedbug  was  killed  and  none  of  the  eggs  showed 
signs  of  hatching  in  12  days.  According  to  experiments  made  by 
the  U.  S.  Public  Health  Service  five  ounces  of  powdered  potas- 
sium cyanide  per  1000  cubic  feet  is  sufficient  for  the  destruction 
of  bedbugs,  four  ounces  for  mosquitoes,  two  and  one-half  ounces 
for  fleas  and  ten  ounces  for  lice. 

Sulphur.  —  The  fumes  of  burning  sulphur,  sulphur  dioxide, 
rank  next  to  hydrocyanic  acid  gas  as  both  a  disinfectant  and  an 
insecticide,  but  they  have  a  serious  disadvantage  in  their  tendency 
to  bleach  fabrics  and  to  tarnish  metals,  especially  in  a  humid 
atmosphere.  Sulphur  dioxide  is  considered  the  most  effective 
remedy  for  mosquitoes  in  cellars,  barns,  etc.,  since  it  kills  these 
insects  even  when  very  dilute,  and  it  has  remarkable  penetrating 
power.  The  methods  of  sealing  rooms  or  buildings  are  similar 
to  those  described  for  hydrocyanic  acid  fumigation.  All  dyed 
goods  and  metallic  articles,  however,  must  be  removed  or  covered 
with  vaseline.  Two  pounds  of  sulphur  is  used  to  1000  cu.  ft., 
more  if  the  building  cannot  be  tightly  sealed.  The  sulphur  is 
placed  in  some  suitable  dish  with  a  little  wood  alcohol  poured  on 
it  to  make  it  burn  more  readily.  In  order  to  avoid  danger  of  fire, 
the  dish  of  sulphur  should  be  placed  on  bricks  or  in  a  tub  of  shal- 
low water  before  igniting.  After  two  hours  the  place  may  be 
opened  and  ventilated. 

Other  Fumigants.  —  Another  effective  insecticide  is  the  vapor 
of  carbon  bisulphide,  a  poisonous  gas  which  is  not  nearly  so 
virulent  as  hydrocyanic  acid  gas.  As  its  vapor  is  heavy  it 
settles  rapidly.  Its  effect  on  many  insects  is  less  certain  than  in 
the  case  of  the  hydrocyanic  acid  gas  and  it  has  the  additional 
disadvantage  of  being  both  inflammable  and  explosive.  Re- 
cently cresyl  or  creolin,  a  very  volatile  substance,  has  come  into 
favor  as  a  fumigating  medium,  especially  for  destroying  mos- 
quitoes. It  is  not  injurious  to  higher  animals  in  the  strength 
used  (125  cc.  to  1000  cubic  feet),  does  not  injure  household  goods 
and  is  destructive  to  all  exposed  insects.  It  is  volatilized  by 
means  of  an  alcohol  lamp.  Cresyl  does  not,  however,  have  the 
penetrating  power  of  hydrocyanic  acid  gas  or  sulphur,  and  is 
therefore  of  less  value  for  such  secretive  insects  as  bedbugs, 
though  highly  valuable  for  exposed  insects,  such  as  mosquitoes, 
since  they  may  be  destroyed  without  having  the  rooms  vacated. 
Formaldehyde,  though  a  valuable  disinfectant,  i.e.,  active  in 
the  destruction  of  microorganisms,  is  not  an  effective  insecticide. 


CHAPTER  XXIII 
LICE 

Although  the  disrepute  of  human  Hce  has  grown  with  civiliza- 
tion and  with  the  knowledge  that  lousiness  and  cleanliness  are 
incompatible,  lice  are  even  yet  among  the  most  important  of 
external  human  parasites.  In  former  times  the  louse  apparently 
was  not  an  object  of  disgust  and  loathing  even  among  the  better 
class  of  people.  In  Herrick's  entertaining  book,  ''  Household 
Insects,"  the  following  quotation  from  Hooke,  an  English  zoolo- 
gist of  the  17th  century,  is  given  concerning  the  head  louse. 
"  This  is  a  creature  so  officious  that  'twill  be  known  to  everyone 
at  one  time  or  another,  so  busie,  so  impudent,  that  it  will  be  in- 
truding itself  into  everyone's  company,  and  so  proud  and  as- 
piring withall  that  it  fears  not  to  trample  on  the  best,  and  affects 
nothing  so  much  as  a  crown;  feeds  and  lives  very  high,  and  that 
makes  it  so  saucy  as  to  pull  anyone  by  the  ears  that  comes  its 
way,  and  will  never  be  quiet  till  it  has  drawn  blood." 

Unfortunately,  even  at  the  present  time,  and  in  the  face  of 
present  knowledge  concerning  the  role  of  lice  in  the  spread  of 
disease,  there  are  many  individuals,  many  communities  and  even 
some  races  which  make  no  effort  to  exterminate  them.  Still 
more  unfortunate  is  it  that  there  are  many  people  who  of  neces- 
sity must  associate  with  these  unwelcome  companions.  In 
logging  camps,  jails,  ships,  railroad  camps,  etc.,  where  close 
association  with  people  who  are  dirty  by  nature  is  unavoidable, 
lice  very  often  become  prevalent.  Most  of  all,  however,  are 
Hce  associated  with  war.  The  deadly  typhus  fever,  which  has 
ravaged  the  armies  of  almost  every  war  in  the  history  of  the  world, 
as  far  as  is  known,  apparently  is  spread  exclusively  by  Hce.  These 
parasites  are  the  guerillas  of  war;  they  bring  suffering  and  death 
not  only  to  armies  but  also  to  the  innocent  non-combatant  popu- 
lation of  the  war-stricken  countries  through  which  the  armies 
have  passed.  This  phase  of  the  subject  will  be  discussed  in  more 
detail  under  the  section  on  "  Lice  and  Disease." 

387 


388 


LICE 


Ttl.'m. 


General  Structure.  — 

Lice  are  small  wing- 
less insects  constituting 
the  order  Siphunculata. 
They  were  formerly  class- 
ified as  a  suborder  of  the 
Hemiptera  or  true  bugs, 
but  recent  studies  have 
shown  the  erroneousness 
of  this  grouping.  The 
mouthparts  are  adapted 
for  piercing  and  sucking. 
The  piercing  apparatus 
(Fig.    171B)    consists   of 

Fig.  171.     Mouthparts  of  a  body  louse;    A,  four    needle-like    organs, 
longitudinal  section  through  head ;  5,  mouthparts  „      u*   u    •     4.U      ^   r 

from  sac  under  pharynx  and  oesophagus;  buc.  t.,  0^^6  01  Wnicn  IS  tne  uell- 
buccal  tube;  m.,  mouth  cavity;  ph.,  pharynx;  oes.,  ^ate  Salivary  duct,  which 
oesophagus;  retr.  sac,  retractile  sack  for  mouth-  ,  '^u  j  •    + 

parts;  prot.  m.,  protractor  muscles  of  pharynx;  Can  be  Wltnarawn  mtO 
ret.  m.,  retractor;  dil.  m.,  dilators;  d.  p.,  dorsal  ^  little   pOUch  Under  the 

ventral  piercer ;  ^^,^       a\ 

(Adapted from  pharynx    (Fig.    171    A). 
This  type  of  mouthparts 


piercer;  sal.  d.,  salivary  duct;  v.  p. 
V.  pi.,  ventral  plate  =  labium  (?). 
Harrison.) 


jaw 


ant,, 


readily  distinguishes  the 
true  lice  from  the  bird 
lice,  which  constitute 
the  order  Mallophaga 
(Fig.  172).  In  the  latter 
there  are  nipper-like 
mandibles  fitted  for  bit- 
ing instead  of  sucking, 
and  these  parasites  feed 
only  on  hair,  feathers, 
etc.,  and  not  at  all  on 
blood.  In  other  respects 
_,,,.,  ^         ,.  , ,     the  sucking  Kce  and  bird 

Fig.   172.     Head   of   bird   louse   (from  golden  ,.  ,  •  i        t_i 

eagle);  ant.,  antenna.  Note  breadth  of  head  as  hce  ShOW  a  considerable 
compared  with  thorax,  a  feature  which  readily  resemblance  t  O  each 
distinguishes  bird  lice  from  sucking  lice. 

other,  and  are  now  gen- 
erally believed  to  be  closely  related.  These  two  orders  of  lice  are 
sometimes  combined  in  an  order  Anoplura.  The  feet  of  the  true 
lice  are  armed  each  with  a  very  large  curved    claw,  quite  gro- 


BODY  LOUSE 


389 


tesque  m  appearance  in  some  species,  which  closes*  back  like  a 
finger  against  a  thumblike  projection  of  the  next  segment  of  the 
leg  (Fig.  173).     There  are  not  even  rudiments  of  wings. 

The  body  of  a  louse  is  clearly  divided  into  head,  thorax  and 
abdomen  (Fig.  174).  The  thorax  is  always  broader  than  the 
head,  a  characteristic 
which  distinguishes  at  a 
glance  a  true  louse  from 
the  broad-headed  bird 
louse  (Fig.  172).  The 
abdomen  is  divided  into 
segments,  normally  eight 
of  them  in  the  human  spe- 
cies; the  terminal  one 
is  indented  in  the  female, 
but  is  rounded  in  the 
male  with  the  large 
spikelike  copulatory  or- 
gan often  projecting  at 

its  tin  fFie"    174    n    '^QO'l     humanus.      Note  huge  claw  and  thumb-like  op- 


FiG.  173.     Front  leg  of  body  louse,  Pediculus 
bte  huge  claw  and  thumb 
posing  process  of  next  segment.      X  100. 


The  digestive  tract,  as  in 
most  other  blood-sucking  insects,  is  furnished  with  capacious 
pouches  branching  from  the  stomach,  which  serve  as  food  reser- 
voirs. The  tracheal  system  is  well  developed  and  opens  by  prom- 
inent spiracles  on  the  sides  of  the  abdomen. 

Most  species  of  lice  are  quite  closely  limited  to  a  single  host, 
and  sometimes  even  genera  are  thus  limited.  Kellogg  has  sug- 
gested that  the  evolutionary  affinities  of  different  birds  and  mam- 
mals may  be  demonstrated  by  the  kinds  of  lice  which  infest  them. 
The  lice  infesting  man  have  generally  been  regarded  as  belonging 
to  three  species,  each  selecting  a  different  portion  of  the  body  as  a 
habitat;  these  are  the  head  louse,  Pediculus  humanus  (capitis), 
the  body  louse,  P.  corporis  (vestimenti) ,  and  the  crab  louse,  Phthi- 
rius  pubis.  The  head  louse  and  body  louse  are  now  thought 
to  be  mere  races  or  varieties  of  a  single  species,  P.  humanus. 
Both  Pediculus  and  Phthirius  are  probably  normally  confined  to 
human  beings. 

Body  Louse.  The  body  louse  (Fig.  174)  is  by  far  the  most 
common,  as  it  is  the  most  important,  louse  infesting  man.  It 
closely  resembles  the  head  louse,  but  is  often  larger,  more  ro- 
bust and  less  active.     Fertile  offspring  result  from  hybridization 


390 


LICE 


"dnt. 


of  these  two'  species.  The  females,  which  are  somewhat  larger 
than  the  males,  reach  a  length  of  about  one-eighth  of  an  inch. 
Due  to  their  dirty  white  or  grayish  color  these  lice  are  familiarly 
known  as  ''  gray-backs."  This  species  is  known  to  be  instru- 
mental in  transmitting  both 
typhus  fever  and  European 
relapsing  fever. 

As  the  name  "body  louse" 
implies,  this  species  inhabits 
the  trunk  rather  than  the 
head.  The  German  name 
'' Kleiderlaus  ",  meaning 
"  clothes  louse  ",  is  still  better, 
since  this  louse  has  so  far 
adapted  itself  to  its  host  as 
to  have  broken  away  from 
the  custom,  prevalent  among 
all  other  species  of  lice,  of 
living  in  the  hair  of  the  body, 
and  to  have  established  the 
habit  of  living  on  the  cloth- 
ing. Just  when,  in  the  proc- 
ess of  our  evolution  from  a 
hairy  ancestor,  this  louse 
shifted  its  position  from  the 
waning  hair  to  the  more  and  more  habitually  worn  clothes  would 
be  interesting  to  know.  Not  unlikely  both  this  louse  and  the 
closely  allied  head  louse  have  evolved  from  a  species  which  once 
roamed  the  hairy  bodies  of  our  forefathers,  each  species  coping 
with  the  unfavorable  circumstance  of  the  developing  hairless- 
ness  of  its  host  in  a  different  way,  the  more  conservative  head 
louse  withdrawing  to  the  fine  hair  of  the  head,  the  body  louse 
adapting  itself  to  living  on  the  clothing. 

A  person  infested  with  thousands  of  body  lice  may  remove  his 
clothing  and  find  not  a  single  specimen  on  his  body.  An  exami- 
nation of  the  underwear  will  reveal  them  adhering  by  their  long 
claws  to  the  surfaces  which  were  next  to  the  body.  Here  they 
live  and  lay  their  eggs,  leaving  the  clothing  only  long  enough  to 
suck  a  meal  of  blood,  even  then  usually  adhering  to  the  clothes 
by  their  hind  legs. 


Fig.  174.  Body  louse,  Pediculus  humanus, 
male;  ant.,  antenna;  e.,  eye;  p.,  penis;  sp., 
spiracles;    th.,  thorax,       X  25. 


LIFE  HISTORY  OF  BODY  LOUSE 


391 


— hciip 


—fibres 


Habits  and  Life  History.  —  Although  there  has  been  very 
close  association  between  lice  and  human  beings  probably  since 
man's  first  appearance  in  the  world,  little  definite  knowledge 
concerning  the  life  history  of  any  of  the  three  species  was  ob- 
tained until  recently.  The  importance  of  lice  in  the  great  anti- 
German  war  has  stimulated  much  research  on  them. 

One  of  the  first  experiments  with  the  breeding  of  body  lice  was 
made  by  the  great  zoological  pioneer,  Leeuenhoek,  in  the  17th 
century.  He  placed  two  female  lice  in  his  stocking  and  tied 
them  in;  after  six  days  he  opened  the  brood  chamber  and  found 
a  cluster  of  50  eggs  beside  one 
of  the  lice  and  another  cluster 
of  40  eggs,  probably  laid  by 
the  other  insect  which  had 
escaped.  He  found  50  more 
eggs  in  the  remaining  louse. 
He  left  the  eggs  in  his  stocking 
ten  days  more,  when  he  dis- 
covered 25  young  lice,  where- 
upon he  abandoned  his  experi- 
ment in  disgust. 

The  eggs  of  lice,  commonly 
called  ''nits,"  are  oval,  whitish 
objects  fitted  with  a  little  lid  at 
the  larger  end,  through  which 
the  hatching  takes  place.  The  eggs  of  the  body  louse  are  about 
one  mm.  dV  oi  an  inch)  in  length.  They  are  glued  to  the  fibers  of 
clothing  (Fig.  175B)  especially  along  seams  or  creases,  although 
in  all  other  lice  the  eggs  are  glued  to  hair.  Under  experimental 
conditions  the  body  louse  will  sometimes  lay  eggs  on  hairs,  but 
it  nearly  always  selects  the  crossing  point  of  two  hairs  and  shows 
less  skill  in  attaching  the  eggs.  The  body  louse  shows  a  marked 
"  homing  "  instinct  in  laying  her  eggs  and  shows  a  strong  desire  to 
lay  eggs  where  others  have  been  laid,  until  clusters  of  from  50 
to  75  or  more  have  been  formed. 

According  to  recent  experiments  by  Sikora  in  Germany  and 
Bacot  in  England,  the  number  of  eggs  laid  by  the  single  female 
body  louse  may  frequently  reach  200  or  more.  Bacot  obtained 
295  eggs  from  a  single  specimen  in  one  case.  During  the  first 
three  or  four  days  only  two  to  four  eggs  are  laid  daily,  the  num- 


FiG.  175.  A,  egg  of  head  louse,  Pedi- 
culus  capitis;  B,  egg  of  body  louse,  P. 
humanus.    X  25.     (After  Cholodkowsky.) 


392  LICE 

ber  gradually  rising,  until  after  a  week  or  so  of  egg-laying  seven 
to  ten  or  more  eggs  may  be  laid  each  day.  A  day  or  two  before 
the  end  of  egg-laying  and  the  death  of  the  louse  the  daily  number 
drops  again.  Eggs  are  laid  whether  copulation  has  occurred 
or  not,  but  in  no  case  have  unfertihzed  eggs  been  observed  to 
develop.  One  copulation  is  not  sufficient  to  fertihze  all  the  eggs, 
but  fertile  eggs  may  be  laid  for  at  least  20  days  after  a  single 
copulation.  According  to  Sikora,  copulation  normally  takes 
place  at  intervals  of  from  one  to  three  days.  Egg-laying  ceases 
at  temperatures  below  77°  F.  and  a  daily  exposure  to  a  tempera- 
ture of  60°  F.  for  only  two  or  three  hours  causes  a  marked  faUing 
off  in  egg  production. 

According  to  Sikora  the  eggs  hatch  in  about  six  days  at  the 
optimum  temperature  of  95°  F.  At  a  temperature  of  77°  F. 
the  incubation  period  is  prolonged  to  16  days,  whereas  at  68°, 
lowered  from  42°  to  60°  F.  during  the  latter  part  of  the  night,  or 
at  a  constant  temperature  of  60°  F.,  no  hatching  at  all  takes  place. 
At  temperatures  above  95°,  also,  the  eggs  suffer  a  high  mortaUty 
probably  due  to  the  difficulty  in  obtaining  proper  conditions 
of  humidity  rather  than  to  the  direct  effect  of  the  heat  itself. 
Either  excessive  humidity  or  complete  drying  is  fatal  to  the 
eggs.  It  is  evident  that  in  winter  the  laying  off  of  the  clothing 
at  night  in  a  cold  room  or  the  leaving  of  mattresses  or  bed  clothes 
in  the  daytime  is  sufficient  to  prevent  the  laying  of  eggs  or  the 
hatching  of  eggs  already  laid,  thus  resulting  in  the  extermination 
of  the  lice. 

The  newly  hatched  lice  are  almost  perfect  miniatures  of  the 
adults,  and  are  ready  to  feed  almost  as  soon  as  they  emerge  from 
the  egg;  in  fact,  they  usually  die  in  less  than  24  hours  if  not 
allowed  to  feed,  though  the  adults  can  survive  as  much  as  five 
days  of  starving.  According  to  Sikora,  the  rapidity  of  the 
development  of  lice  is  dependent  on  temperature  and  on  amount 
of  food.  At  a  temperature  of  95°  F.  and  with  as  many  daily 
feeds  as  would  willingly  be  taken,  namely  six,  the  lice  pass  through 
their  first  moult  in  three  days,  the  second  in  five  or  six  days,  and 
the  third,  which  brings  them  to  maturity,  in  eight  or  nine  days. 
Reduction  of  daily  feeds  to  two  increased  the  period  of  develop- 
ment to  nine  or  ten  days,  whereas  reduction  of  temperature  to 
75°  F.  by  day  and  95°  F.  by  night,  with  two  daily  feeds,  prolonged 
the  development  to  from  13  to  15  days. 


HABITS  OF  BODY  LOUSE  393 

According  to  observations  by  Sikora,  copulation  may  take 
place  within  ten  hours  after  the  last  moult  has  been  passed,  and 
Bacot  also  observed  cases  in  which  copulation  took  place  on  the 
day  of  reaching  maturity.  Egg-laying  begins  in  from  one  to  four 
days  after  the  final  moult  and  continues  at  the  rate  described 
on  the  preceding  page  until  the  death  of  the  insect.  The  aver- 
age length  of  life  for  the  females  is  about  35  or  40  days,  and 
probably  a  little  less  for  the  males. 

According  to  Bacot,  hungry  lice  do  not  show  a  tendency  to 
wander  on  the  skin,  but  proceed  to  pierce  the  skin  and  suck  blood 
at  once.  Nor  do  they  shift  to  make  another  stab,  as  fleas  fre- 
quently do,  if  the  first  stab  does  not  immediately  furnish  blood. 
They  apparently  place  great  reliance  on  the  power  of  the  sali- 
vary secretion,  which  is  poured  into  the  wound,  to  dilate  the 
capillaries  by  its  irritation  and  thus  cause  a  flow  of  blood.  Some- 
times blood  is  not  drawn  for  several  minutes  after  the  puncture 
is  made.  Bacot  states  that  lice  fill  their  crops  in  from  two  to 
15  minutes,  but  Sikora  observed  that  adult  lice,  if  fed  only  twice 
daily,  sucked  for  an  hour  to  an  hour  and  a  half,  and,  if  left  in  con- 
tact with  the  skin  for  several  hours,  have  a  tendency  to  pump 
blood  intermittently  with  short  pauses,  meanwhile  voiding  ex- 
crement containing  undigested  blood  corpuscles.  Sikora  also 
observed  that  hungry  lice  placed  on  the  well-shaved  skin  of  a 
puppy  made  repeated  attempts  to  draw  blood  without  success, 
and  also  that  dog  lice,  HcBmatopinus  ventricosus,  tried  in  vain  to 
draw  blood  from  the  human  skin.  He  concludes  therefrom 
that  not  only  is  it  necessary  for  lice  to  penetrate  the  skin  with 
their  piercing  apparatus,  but  that  they  must  also  produce  an 
irritation  by  means  of  a  salivary  secretion,  apparently  specific 
in  its  action  for  certain  kinds  of  blood,  in  order  to  cause  blood 
to  flow  from  the  tiny  puncture.  Apparently  the  salivary  se- 
cretion deteriorates  in  unfed  lice,  for  though  starved  lice  may 
still  be  able  to  drive  their  piercing  apparatus  into  the  skin,  it 
takes  them  three  times  as  long  to  draw  blood. 

A  fact  of  far-reaching  significance,  if  found  to  be  commonly  true, 
has  recently  been  reported  by  Hall  in  Texas.  This  author 
found  that  a  female  body  louse  taken  from  a  Mexican  baby, 
when  placed  in  a  bottle  with  a  head  louse  taken  from  the  same 
baby,  devoured  the  head  louse.  Two  head  Uce  were  then  fed 
to  the  body  louse  daily  for  three  days,  and  the  same  louse  was 


394  LICE 

induced  to  eat  crab  lice,  small  black  ants,  bedbugs,  and  raw  beef. 
When  body  lice  were  placed  in  a  bottle  with  head  lice,  bedbugs, 
and  a  piece  of  beef,  they  ate  first  the  head  lice,  then  the  bedbugs 
then  the  beef,  and  finally  became  cannibals  to  the  extent  of  the 
survival  of  the  fittest!  This  would  readily  explain  such  facts 
as  that  body  lice  (according  to  Hall)  can  be  found  in  empty  box 
cars  used  to  transport  Mexican  troops  weeks  before,  and  it 
would  account  for  louse-borne  diseases  lying  dormant  in  isolated 
places.  A  freight  car  once  infected  with  typhus  would  be  a  source 
of  danger  for  a  longer  period  than  the  few  days  a  louse  can  live 
without  food.  However,  before  insectivorousness  can  be  ad- 
mitted as  a  usual  habit  of  lice  in  the  absence  of  normal  food, 
further  investigation  is  necessary. 

Digestion  is  very  rapid.  An  entire  two-hour  feed  may  be 
digested  in  from  eight  to  ten  hours  at  95°  F.,  but  digestion  is 
slower  at  lower  temperatures  and  the  stomach  contents  remain 
unchanged  for  ten  hours  or  more  at  45°  F.  or  below.  At  tem- 
peratures above  95°  F.  digestion  is  even  more  rapid,  but  there  is 
a  high  mortality. 

It  is  evident  from  Sikora's  experiments  that  95°  F.  is  the  op- 
timum temperature  for  the  development  and  reproduction  of 
lice.  The  absence  of  lice  from  hot  countries  —  observable  in 
Mexico,  for  instance,  where  they  are  abundant  on  the  central 
plateau  above  5000  to  6000  feet,  but  absent  from  the  hot  coastal 
strips  —  is  apparently  not  due  to  the  high  temperature  but 
probably  to  the  disastrous  effect  of  profuse  perspiration  and 
consequent  excessive  humidity  between  the  clothes  and  skin. 

The  bites  of  the  body  louse  produce  itching  red  pimples  which 
become  covered  by  a  brownish  crust,  the  results  of  the  action 
of  the  toxic  salivary  juices.  Scratching  produces  characteristic 
white  scars,  surrounded  by  brownish  pigment;  in  fact,  large 
areas  of  the  skin  may  take  on  a  mottled  bronze  color.  The  color- 
ing of  the  skin  is  said  to  be  due  to  the  stimulation  of  pigment 
formation  in  the  skin  by  toxins  secreted  by  the  louse.  Many 
individuals  develop  an  insensibility  to  the  bites  of  lice,  a  fact 
which  probably  explains  the  indifference  of  some  communities 
to  them  as,  for  instance,  the  people'  of  Russian  Poland. 

Head  Louse.  The  head  louse,  P.  humanus  capitis,  is  very 
closely  related  to  the  body  louse,  and  is,  in  fact,  thought  by  some 
workers  to  be  a  mere  variety  of  the  latter.     Aside  from  its  different 


HEAD  LOUSE  396 

habits,  however,  it  differs  very  slightly  from  its  relative.  It  is 
commonly  smaller  in  size,  and  is  more  distinctly  festooned  along 
the  sides,  due  to  constrictions  at  the  joints  between  the  segments. 
Nuttall,  however,  has  shown  that  all  of  the  supposed  morpho- 
logical and  biological  differences  between  these  two  kinds  of  lice 
are  inconstant,  and  they  should,  therefore,  be  considered  as 
races  of  a  single  species.  The  head  louse  assumes  all  the  char- 
acteristics of  the  body  louse  when  reared  under  conditions  suit- 
able for  the  latter. 

The  head  louse  although  usually  preferring  the  fine  hair  of  the 
head  as  a  habitat  occasionally  wanders  to  other  parts  of  the  body 
as  well.  It  is  found  in  every  part  of  the  world.  Different  vari- 
eties are  said  to  occur  on  the  different  human  races  and  to  vary 
in  color  with  the  color  of  the  skin  on  which  they  live.  The 
lice  which  live  on  the  white  race  are  pale  gray  with  a  dark  line 
along  each  side  of  the  abdomen,  those  on  negroes  are  blackish 
or  brown,  on  Hindoos  smoky  brown,  on  Japanese  and  Chinese 
yellowish,  and  on  American  Indians  dark  reddish  brown.  What 
a  wonderful  case  of  protective  coloration,  except  that,  as  in  so 
many  other  cases  of  so-called  protective  coloration,  there  is  no 
practical  protection.  A  negro  is  as  likely  to  scratch  out  a  black 
louse  as  a  white  one! 

As  in  the  case  of  the  body  louse  reproduction  is  very  rapid  but 
the  egg  production  is  lower,  due  to  the  smaller  capacity  of  the 
body,  even  taking  into  consideration  the  slightly  smaller  size 
of  the  eggs.  The  course  of  development  is  practically  the  same 
in  both  species.  The  average  number  of  eggs,  according  to 
Bacot's  observations,  is  from  80  to  100.  Only  one  mature  egg 
can  be  developed  in  the  louse's  body  at  a  time,  but  the  suc- 
cession of  them  is  so  rapid  that  eight  or  ten  may  be  laid  in  a 
day.  Each  egg  or  "  nit  "  is  glued  by  the  lower  end  to  a  hair 
(Fig.  175 A),  the  favorite  "  nests  "  being  the  vicinity  of  the  ears. 
The  young  lice  hatch  in  ten  or  12  days  and  reach  maturity  in 
two  or  three  weeks,  and  are  then  ready  to  reproduce  again.  At 
this  rate  of  reproduction,  allowing  only  a  50  per  cent  hatch,  a 
single  pair  of  lice  theoretically  could  produce  over  three-quarters 
of  a  miUion  offspring  in  the  fourth  generation,  and  in  the  course 
of  less  than  three  months! 

Although  the  bites  of  this  species  are  not  quite  so  irritating  as 
are  those  of  the  body  louse,  yet  the  frequent  piercing  of  the  skin 
for  a  gory  meal  results  in  much  scratching.  Often  the  bites 
swell  into  pimples  which  may  bleed  when  scratched    or  which 


396  LICE 

form  a  little  pus,  sufficient  in  very  negligent  individuals  to  make 
the  hair  mat  together.  According  to  Stiles,  if  this  is  allowed  to 
run  on,  a  regular  carapace  may  form,  called  trichoma,  in  which 
fungous  growths  may  develop,  and  under  which  the  lice  abound, 
and  the  head  may  exude  a  foetid  odor. 

Crab  Louse.  —  The  crab  louse,  Phthirius  pubis  (Fig.  176),  is 
quite  distinct  from  the  other  two  species  of  human  lice.  It  has 
a  very  broad  short  body  with  long,  clawed  legs,  presenting  the 
general  appearance  of  a  tiny  crab,  from  which  it  derives  its  name. 
The  first  pair  of  legs  are  smaller  than  the  others  and  do  not 


Fig.  176.     Crab  louse,  Phthirius  pubis,  9 .      X  35. 

possess  a  *'  thumb  "  in  apposition  to  the  curved  claw.  The 
abdomen  is  composed  of  six  segments,  and  is  markedly  festooned 
along  the  sides.  This  louse  is  grayish  white  in  color,  with  dark 
shoulder  patches  and  slightly  reddish  legs.  The  females  are 
about  yV  of  an  inch  in  length,  the  males  somewhat  smaller.  The 
favorite  haunts  are  the  pubic  regions  and  other  parts  of  the  body 
where  coarse  hair  grows,  as  in  the  armpits  and  in  the  beard  and 
eyebrows.  Unlike  the  other  human  lice  this  species  is  almost 
exclusively  confined  to  the  Caucasian  race. 

The  females  produce  from  ten  to  15  eggs  and  glue  them,  one 
at  a  time,  to  the  coarse  hairs  among  which  they  live.     A  number 


LICE  AND  DISEASE  397 

of  eggs  may  be  glued  to  a  single  hair,  and  often  at  some  distance 
from  the  skin.  The  eggs  hatch  in  six  or  seven  days,  and  the  young 
become  sexually  mature  in  about  15  days.  This  species,  even 
under  favorable  conditions,  will  live  apart  from  its  host  only 
ten  or  12  hours.  The  eggs  are  said  not  to  develop  except  at 
temperatures  between  68°  F.  and  86°  F.,  which  are  approxi- 
mately the  temperatures  to  which  eggs  attached  to  hairs  beneath 
the  clothing  would  be  exposed. 

Lice  and  Disease 

The  role  of  lice  in  the  spread  of  disease  has  long  been  sus- 
pected in  an  indefinite  and  uncertain  way.  Only  recently,  and 
at  the  cost  of  the  lives  of  several  great  investigators,  has  the 
whole  portentous  truth  regarding  the  transmission  by  them  of 
typhus  and  relapsing  fever  (North  African  and  European  types) 
been  brought  to  light.  Foremost  among  the  investigators  of 
louse-borne  diseases  stands  the  name  of  NicoUe  and  his  associates, 
who  in  1909  proved  that  typhus  fever  could  be  transmitted  by 
the  body  louse,  and  in  1913  that  the  Algerian  type  of  relapsing 
fever  could  be  transmitted  likewise.  Two  American  investi- 
gators, Ricketts  and  Wilder,  working  independently  of  the  French 
workers,  proved  in  1910  that  the  body  louse  was  instrumental 
in  transmitting  typhus  (tarbardillo)  in  Mexico,  and  in  1912 
Anderson  and  Goldberger  showed  that  the  head  louse  could  also 
transmit  it.  Opinions  differ  as  to  whether  the  infection  can  be 
transmitted  through  the  eggs  to  the  lice  of  the  succeeding  genera- 
tion. In  1918  an  American  commission  under  Dr.  R.  P.  Strong, 
and  a  British  committee  under  Sir  David  Bruce  and  Major  Byam, 
working  under  field  conditions  on  the  war  front  in  France,  dem- 
onstrated that  trench  fever  is  a  louse  borne  disease. 

There  is  every  reason  to  belive  that  typhus  fever  is  normally 
transmitted  exclusively  by  lice.  Wherever  the  hording  together 
of  promiscuous  crowds  of  people  becomes  necessary  and  when 
scrupulous  cleanliness,  either  of  necessity  or  of  choice,  is  not  en- 
forced, there  the  lice  will  thrive  and  sooner  or  later  the  dread 
disease  will  break  out.  The  organism  which  is  believed  to  be 
the  cause  of  typhus  fever,  Rickettsia  prowazeki,  is  discussed  on 
p.  186.  NicoUe  and  his  fellow  workers  have  shown  that  lice  which 
are  fed  on  infected  patients  do  not  become  infective  until  the 
eighth  and  usually  the  ninth  or  tenth  day  afterward.     The  same 


398  LICE 

results  were  obtained  both  in  experiments  with  crushed  Hce  and 
with  the  excrement  of  the  hce. 

Epidemics  of  typhus  usually  occur  in  winter  and  in  cold  coun- 
tries, due  to  the  huddling  together  of  people  in  warm,  poorly 
ventilated  houses  where  lice  thrive,  and  where  the  unhygienic 
conditions  lower  the  vitality  of  the  people.  Typhus  has  fol- 
lowed in  the  wake  of  nearly  every  army  which  has  ever  been 
assembled.  During  the  present  great  European  war  typhus 
has  been  largely  absent  from  the  armies  and  population  of  Brit- 
ain, France  and  Germany,  due  solely  to  the  intensive  anti-louse 
measures  which  have  been  enforced  by  these  countries.  The 
less  scientific  and  less  cleanly  nations  have  suffered  enormous 
losses.  An  epidemic  began  in  Serbia  in  January,  1915,  among 
some  Austrian  prisoners  who  were  allowed  to  disperse  all  over 
the  country.  The  disease  spread  with  them,  and  for  a  time  raged 
almost  at  will  in  that  war-stricken  country.  The  majority  of 
the  small  number  of  Serbian  doctors  were  affected,  no  sanitary 
measures  for  the  suppression  of  lice  were  understood  or  enforced, 
and  no  adequate  accommodations  for  the  sick  could  be  provided. 
The  epidemic  continued  to  rise,  and  reached  its  height  in  April, 
when  there  were  estimated  to  be  9000  deaths  per  day.  It  was 
largely  through  the  heroic  efforts  of  the  American  Red  Cross 
expedition  that  the  epidemic  was  finally  checked,  after  having 
destroyed  over  150,000  people.  In  December,  1916,  another 
epidemic  was  reported  to  be  raging  in  Syria  with  over  1000  deaths 
per  day.  Milder  epidemics  have  occurred  in  Austria,  Bulgaria 
and  Russia,  all  countries  where  science  and  cleanliness  have 
not  been  worshipped  as  they  have  in  the  greater  nations  of  Eur- 
ope. Mexico  has  suffered  also;  in  December,  1915,  11,000 
cases  of  typhus  were  reported  in  Mexico  City  and  its  environs. 

The  role  of  lice  in  the  transmission  of  the  European  and  North 
African  form  of  relapsing  fever  has  long  been  suspected  but  was 
not  proved  until  1913,  when  NicoUe  and  his  fellow- workers 
scientifically  demonstrated  it  in  Tunis  and  Algeria.  Noting 
that  the  louse  was  the  only  constant  factor  affecting  the  occur- 
rence of  the  disease,  these  French  workers  undertook  extensive 
experiments  which  resulted  in  proving  that  the  body  louse,  and 
probably  also  the  head  louse,  serves  as  a  medium  for  the  develop- 
ment of  the  spirochaetes  of  relapsing  fever,  and  that  these  insects 
transmit  the  disease  not  by  biting  but  by  inoculation  of  the 


TRANSMISSION  OF   DISEASES  399 

wounds  which  they  make  with  the  infected  contents  of  their 
bodies  when  crushed. 

Nicolle  and  his  associates  also  showed  that  sometimes,  at  least, 
the  spirochsetes,  probably  in  the  granule  stage,  are  hereditarily 
transmitted  through  the  eggs  to  the  young  of  the  next  generation, 
as  is  the  case  with  the  African  relapsing  fever  parasites  in  the 
tick.  Experiments  on  the  transmission  of  the  relapsing  fever  of 
Algeria  with  other  parasites  such  as  bedbugs,  fleas,  biting  flies 
and  ticks  were  negative.  Some  observers,  however,  believe  that 
in  Europe  other  insects  also,  notably  bedbugs,  may  be  instru- 
mental in  transmitting  relapsing  fever.  The  evidence  furnished 
by  the  epidemiology  of  the  disease  is,  however,  very  strongly  in 
favor  of  lice  as  the  normal  transmitters.  The  Indian  form  of 
relapsing  fever  is  also  probably  transmitted  by  lice.  Further 
details  of  the  development  of  the  spirochsetes  in  the  lice  are 
given  in  Chapter  IV,  p.  44. 

Being  transmitted  by  lice,  relapsing  fever  shows  the  same  pe- 
culiarities of  occurrence  as  does  typhus;  epidemics  always  rage 
fiercest  in  winter,  and  usually  break  out  during  war  times.  Ser- 
bia, which  was  so  stricken  by  typhus,  was  held  in  the  grip  of  an 
epidemic  of  relapsing  fever  earlier  in  the  war. 

The  demonstration  of  the  relation  of  lice  to  the  transmission 
of  trench  fever  in  1918  by  American  and  British  Commissions 
working  under  war  conditions  was  a  very  brilliant  piece  of  medical 
research  carried  out  successfully  in  spite  of  adverse  conditions. 
For  the  two  years  preceeding  the  beginning  of  the  investigation 
concerning  the  transmission  of  the  disease,  trench  fever  is  said 
to  have  occasioned  more  sickness  among  the  troops  in  France 
than  any  other  infectious  disease.  The  work  of  the  Commissions 
showed  that  trench  fever  is  naturally  transmitted  by  the  body 
louse,  and  that  this  is  the  important  and  common  means  of  trans- 
mission. The  louse  may  transmit  the  disease  by  its  bite  alone, 
or  by  infection  of  abraded  sink  by  the  excrement.  A  discussion 
of  Rickettsia  quintana,  the  probable  cause  of  trench  fever,  and  its 
occurrence  in  infected  lice  will  be  found  on  p.  187. 

Lice  may  also  serve  as  mechanical  transmitters  of  still  other 
diseases.  The  bacilli  of  bubonic  plague  have  been  found  alive 
in  both  body  lice  and  head  lice  taken  from  victims  of  the  disease, 
and  both  this  species  and  the  body  louse  have  been  experimen- 
tally proved  to  be  able  to  transmit  plague  from  rodent  to  rodent 
in  Java.     De  Raadt  in  Java  infected  rodents  with  plague  by  in- 


/ 


400  LICE 

jecting  them  with  ground  bodies  of  head  Hce  taken  from  plague 
patients.  The  practice  among  some  natives  of  kiUing  Hce  by 
mashing  them  against  the  head  of  the  host,  accompanied  by  the 
frequent  scratching  due  to  irritation  from  bites,  may  well  be  a 
frequent  cause  of  plague  infection  if  there  has  been  any  oppor- 
tunity for  the  lice  to  migrate  from  an  infected  to  a  healthy  person. 

There  is  no  reason  why  syphilis  could  not  be  transmitted  in 
a  similar  manner,  especially  during  the  second  stage  of  the  dis- 
ease, when  the  spirochaetes  are  present  throughout  the  blood. 
The  readiness  with  which  spirochaetes  of  other  kinds  will  live  in 
insect  or  tick  bodies  makes  it  reasonable  to  believe  that  the 
spirochaetes  of  syphilis  might  live  in  the  bodies  of  human  lice, 
at  least  long  enough  to  be  conveyed  from  person  to  person. 

Prevention  and  Remedies.  —  The  prevention  of  lousiness  con- 
sists primarily  in  personal  cleanliness.  However,  no  amount 
of  personal  hygiene  and  cleanliness  will  prevent  temporary 
lousiness  if  there  is  association  with  unclean  and  careless  com- 
panions. Lousiness  and  human  wretchedness  and  degradation 
have  always  been  companions,  but  this  does  not  imply  that  lice 
have  any  inherent  abhorrence  of  a  clean  body  if  they  can  get 
access  to  it.  From  the  nature  of  their  habitats  the  common 
modes  of  infection  of  the  three  different  species  of  human  lice 
vary  somewhat.  Any  of  them  will  spread  by  contact  or  close 
association,  but  each  has  its  own  special  means  of  finding  new 
hosts.  The  head  louse  depends  largely  for  distribution  on  a 
promiscuous  use  of  combs  and  brushes  or  borrowed  hats  and 
caps,  and  on  the  free-for-all  trying  on  of  head  gear  in  haberdash- 
eries and  millinery  shops.  The  body  louse  is  dispersed  by  cloth- 
ing and  bed  linen  and  finds  fresh  hunting  grounds  by  night 
migrations  from  one  pile  of  clothes  to  another.  The  crab  louse 
frequently  utilizes  public  toilets  for  dissemination.  Where  men 
are  crowded  together  in  prisons  or  war  camps  lousiness  is  almost 
sure  to  develop  unless  particularly  guarded  against,  since  some 
uncleanly  persons  are  nearly  always  in  the  aggregation,  and  con- 
ditions are  such  that  the  infestation  is  given  every  opportunity 
to  spread.  There  are,  however,  many  ways  in  which  lice  may 
be  dispersed  among  clean  people  in  ordinary  life.  Stiles  reports 
a  case  where  a  large  number  of  girls  in  a  fashionable  boarding 
house  in  eastern  United  States  developed  lousiness  shortly  after 
traveling  from   Chicago   to   New  York  in  a  Pullman   sleeper. 


PREVENTION  OF  LOUSINESS  401 

In  Washington  and  other  cities  where  negresses  do  much  of  the 
laundering  the  family  wash  is  a  common  source  of  infestation. 
Closely  packed  street  cars,  school  cloak  rooms,  unclean  rooming 
houses  —  all  these  and  many  other  means  may  serve  to  start 
a  new  colony  of  lice. 

Perfect  cleanliness  will  usually  result  in  their  quick  elimination. 
A  shampoo  with  warm  water  and  soap,  frequent  baths,  clean 
underclothes,  pressed  suits,  and  other  items  of  personal  care  are 
inimical  to  the  welfare  of  the  unwelcome  visitors.  Certain 
remedies  are,  however,  useful  in  the  quick  destruction  of  these 
pests.  Head  lice  can  best  be  destroyed  by  a  thorough  washing  of 
the  head  with  a  two  per  cent  carbolic  acid  solution  or  a  kerosene 
emulsion  (equal  parts  kerosene  and  olive  oil).  When  one  of 
these  remedies  has  been  thoroughly  rubbed  into  the  hair  the 
head  should  be  covered  with  a  cloth.  After  several  hours  the 
ointment  is  washed  off  in  warm  water  and  ^oap  and  the  dead 
lice  removed  with  a  fine-tooth  comb.  In  long  hair  this  treat- 
ment is  applied  by  having  the  patient  lie  down  with  the  hair 
hanging  over  the  edge  of  a  bed  into  a  pan  of  the  carbolic  solution 
or  kerosene  emulsion,  the  hair  being  sluiced  backward  and  forward 
for  ten  minutes  until  thoroughly  saturated.  The  treatment  may 
have  to  be  repeated  after  about  ten  days  to  destroy  lice  which 
have  hatched  in  the  meantime,  but  usually  the  eggs  are  des- 
troyed as  well  as  the  adult  lice.  Crab  lice  can  be  destroyed  best 
by  the  use  of  mercurial  ointment  applied  to  the  infected  parts, 
accompanied  by  washing  with  soft  soap  and  warm  water.  A 
close  clipping  of  the  hair  in  the  infested  regions  is  the  safest  and 
quickest  method  of  getting  rid  of  the  nits. 

Eradication  of  body  lice  is  in  some  respects  simpler  than  that 
of  other  lice,  since  it  is  the  clothes  instead  of  the  body  which  are 
to  be  treated.  Much  work  has  been  done  since  the  outbreak  of 
the  war  in  Europe  on  testing  the  effect  of  various  chemicals  and 
methods  of  treatment  on  lice.  This  problem  is  recognized  as 
one  of  the  most  important  minor  considerations  in  war. 

The  methods  usually  employed  for  getting  rid  of  body  lice  are 
to  sterilize  the  clothes,  either  by  steam,  by  fumes  of  carbon  bi- 
sulphide or  sulphur  dioxide  (if  no  wool  is  present),  by  dry  heat  of 
160°  F.,  or  by  treatment  with  volatile  odorous  substances,  such  as 
kerosene,  naphthaline,  ether,  anise  oil,  oil  of  turpentine,  oil  of 
eucalyptus  or  anisol  (methylphenylether).     The  last  is  a  new 


/ 


402  LICE 

remedy  reported  by  Frankel,  and  is  said  to  stun  lice  in  four 
minutes  and  to  kill  them  in  ten  minutes.  Soaking  for  one  hour 
in  a  1 J  per  cent  cresol  solution  is  said  to  destroy  all  lice  on  clothing. 
The  eggs  are  not  so  easily  destroyed  as  are  the  adults,  but  they 
succumb  to  heating,  to  exposure  to  carbon  bisulphide  (100  grams 
per  cubic  meter),  or  to  immersion  in  any  of  the  oils  mentioned 
above.  Ammonia  gas  destroys  the  eggs  on  clothing  in  a  closed 
receptacle.  On  the  Mexican  border  of  the  United  States  a  mix- 
ture of  vinegar  and  kerosene  is  used  for  dipping  louse-infested 
clothing.  The  French  soldiers  are  said  to  have  kept  largely  free 
of  lice  by  the  simple  expedient  of  having  a  hot  iron  run  along  the 
seams  of  the  underwear  when  laundered,  to  kill  nits. 

Preventive  measures  against  lice,  simple  as  they  are  under 
ordinary  conditions,  often  constitute  a  very  difficult  problem, 
especially  in  army  camps.  Common  methods  employed  are  the 
treatment  of  the  clothes  with  odorous  or  poisonous  substances, 
the  use  of  underclothes  with  smooth  inner  surface,  such  as  silk 
or  oil  cloth,  to  which  lice  cannot  attach  their  eggs,  or  the  dusting 
of  naphthaline  powder  into  the  shoes,  stockings  and  underwear. 
A  substance  which  has  been  found  most  efficient  by  the  British, 
and  has  been  used  extensively  on  the  western  front  in  France  is 
the  now  famous  NCI,  a  powder  consisting  of  96  per  cent  com- 
mercial naphthaline  with  two  per  cent  creosote  added  to  increase 
the  toxicity  and  to  give  lasting  qualities  and  two  per  cent  iodoform 
to  increase  the  adhesiveness  of  the  powder  when  dusted  on  the 
inside  of  the  clothing.  The  shepherd  people  of  the  Carpathians 
are  said  to  protect  themselves  against  lice  by  saturating  their 
underclothes  in  melted  butter  which  prevents  the  lice  from 
fastening  their  eggs  to  the  fibers  of  the  clothes,  and  probably  the 
fatty  acids  of  rancid  butter  are  also  directly  deleterious  to  the 
pests. 

When  louse  prevention  is  undertaken  on  a  large  scale,  as  it 
has  been  as  never  before  in  the  present  war,  enormous  difficulties 
are  encountered,  largely  due  to  the  fact  that  the  soldiers,  es- 
pecially of  the  less  enlightened  nations,  do  not  cooperate  with 
the  officials.  Germany,  menaced  by  louse-borne  diseases  more, 
perhaps,  than  any  others  of  the  principal  warring  nations,  due  to 
the  constant  contact  of  her  troops  with  the  less  efficiently  cared- 
for  troops  of  Russia  and  of  the  Baltic  nations,  has  largely  solved 
the  problem  by  the  erection  of   ''  disinfection  stations."     In 


DISINFECTION  STATIONS  403 

October,  1915,  there  were  eight  of  these  on  the  Polish  front, 
and  more  were  being  built.  Through  these  stations  men  are 
passed  as  clothes  might  be  passed  through  a  laundry.  Enter- 
ing at  the  "  unclean  side,"  dirty,  lousy  and  unhygienic,  they 
emerge  from  the  ''  clean  side  "  fresh,  clean  and  free  from  ver- 
min. Each  institution  consists  of  eight  separate  buildings, 
grouped  around  a  central  power  house  in  which  200  tons  of  coal 
are  burned  daily  to  supply  steam  for  disinfection,  light,  power, 
etc.  Laundries,  kitchens  and  administrative  quarters  are  also 
provided.  Each  of  the  eight  buildings  consists  of  a  clean  and 
an  unclean  part,  with  a  chief  surgeon  in  charge,  and  each  has  a 
capacity  of  500  men  every  eight  hours,  a  total  of  12,000  per  24 
hours  for  the  entire  institution.  At  the  entrance  on  the  unclean 
side  each  man  receives  a  net  for  whatever  apparel  he  may  have, 
such  as  boots,  helmets,  etc.,  which  must  be  sterilized  by  dry  heat, 
and  a  smaller  net  to  receive  his  valuables,  such  as  notebooks, 
tobacco,  etc.  A  check  number  is  hung  about  his  neck,  and  a 
similar  number  placed  on  his  belongings.  He  is  now  given  a 
pair  of  slippers,  and  enters  a  large  waiting  room  where  he  disrobes, 
placing  his  clothes  in  another  net  which  has  been  given  him,  to 
be  sterilized  by  steam.  If  in  need  of  it  he  is  given  a  hair-cut  and 
is  then  subjected  to  a  fifteen  minute  shower  bath  with  soap,  after 
which  he  is  presented  with  a  towel,  clean  slippers  and  clean  under- 
wear. He  is  then  allowed  to  pass  to  the  clean  side  of  the  build- 
ing where  he  is  given  his  own  disinfected  clothing,  given  a  meal 
and  conducted  to  disinfected  railroad  coaches.  The  greatest 
disadvantage  is  the  non-cooperation  of  Russian  prisoners,  who 
by  all  sorts  of  subterfuges  try  to  avoid  being  *'  laundered." 
However,  Germany  has,  by  this  method,  practically  converted 
her  whole  eastern  front  into  a  huge  filter  to  guard  against  lice 
and  lice-borne  diseases.  Without  such  radical  measures  Ger- 
many could  never  have  kept  herself  as  free  as  she  has  from  the 
diseases  of  war. 


CHAPTER  XXIV 
FLEAS 

David  Harum  says,  ''  A  reasonable  amount  of  fleas  is  good 
for  a  dog.  They  keep  him  from  broodin'  on  bein'  a  dog."  A 
goodly  supply  of  fleas  might  likewise  keep  man  from  brooding  over 
anything  deeper  than  the  presence  of  these  fleas,  but  in  many 
cases  this  in  itself  is  a  rather  serious  thing  to  brood  over.  Not 
only  are  fleas  very  annoying  pests  and  a  common  cause  of  in- 
somnia, but  they  may  also  serve  as  the  disseminators  of  a  number 
of  serious  human  diseases,  among  which  the  terrible  bubonic 
plague  stands  foremost. 

General  Structure.  —  Fleas  are  insects  which  are  more  or  less 
distantly  related  to  the  Diptera  or  two-winged  flies,  but  which 
have  become  so  specialized  by  their  particular  mode  of  life  as 
external  parasites  as  to  necessitate  their  segregation  into  a  dis- 
tinct order  of  their  own,  the  Siphonaptera.  Their  bodies  are 
ordinarily  much  compressed  to  facilitate  gliding  between  the 
hairs  or  feathers  of  their  hosts.  The  head  is  broadly  joined  to 
the  thorax,  which  is  relatively  small.  The  abdomen  is  large  and 
much  compressed  from  side  to  side;  it  consists  of  ten  segments, 
the  first  seven  of  which  are  simple  rings,  each  protected  by  two 
horny  plates,  a  dorsal  "  tergum  "  and  a  ventral  "  sternum  " 
(Fig.  177).  The  last  three  segments  are  modified  differently  in 
the  male  and  female  in  connection  with  the  sexual  organs.  In 
both  sexes  the  "  tergum  "  of  the  ninth  segment  has  a  pitted  area 
covered  with  little  bristles  which  is  called  the  pygidium,  and  is 
probably  sensory  in  function.  All  parts  of  the  body  are  furnished 
with  backward-projecting  bristles  and  spines  which  aid  the  flea 
in  forcing  his  way  between  dense  hairs  and  in  preventing  him  from 
slipping  backward.  The  efficiency  of  these  spines  is  apparent 
when  one  attempts  to  hold  a  flea  between  his  fingers.  Many 
fleas  have  specially  developed,  thick,  heavy  spines  arranged 
in  rows  suggestive  of  the  teeth  of  combs  and  therefore  known  as 
ctenidia  or  "  combs  "  (Fig.  179).     Such  a  comb  may  be  present 

404 


STRUCTURE  405 

either  along  the  ventral  margin  of  the  head  or  along  the  hind 
edge  of  the  pronotum  (the  dorsal  plate  covering  the  first  segment 
of  the  thorax)  or  in  both  places.  The  presence  or  absence  of 
these  combs  and  the  number  of  teeth  in  them  is  of  considerable 
use  in  identification  of  species. 

The  legs  of  fleas  are  very  long  and  powerful,  and  at  first  glance 
seem  to  possess  one  more  segment  than  do  the  legs  of  other  in- 


FiG.  177.     The  Indian  rat  flea,  Xenopsylla  cheopis,  male.     X  50.     (After  Jordan 

and  Rothschild.) 

sects.  They  really  consist  of  the  usual  number  of  segments, 
however,  but  are  pecuHar  in  the  enormous  development  of  the 
first  segments  of  the  legs  (coxae),  which  in  most  insects  are  quite 
insignificant  (Fig.  179).  The  shape  of  the  sternal  plate  to  which 
the  coxae  are  attached  is  suggestive  of  still  another  segment. 
The  great  development  of  the  coxae  as  well  as  of  the  other  seg- 
ments of  the  leg  gives  unusual  springiness  and  consequently 
enormous  jumping  power.  The  human  flea,  Pulex  irritans,  has 
been  observed  by  Mitzmain  to  jump  13  inches  horizontally  and 
seven  and  three-fourths  inches  vertically.  An  equivalent  jump 
for  a  man  of  average  height  would  be  over  450  feet  horizontally 
and  over  275  feet  vertically!  The  jumping  power  must  over- 
come to  some  extent  the  disadvantage  of  winglessness  and  render 
migration  from  host  to  host  comparatively  easy.     All  the  legs 


406  FLEAS 

are  furnished  with  rows  of  stout  spines  and  are  armed  at  the 
tip  with  a  pair  of  large  stout  claws. 

Eyes  are  present  in  some  species  of  fleas  but  not  in  others. 
The  antennae  are  short  and  club-shaped,  and  when  not  in  use  are 
folded  back  into  special  grooves  for  them  on  the  sides  of  the 
head  (Fig.  178,  ant.  gr.).  The  mouthparts  (Fig.  178)  are  fitted 
for  piercing  and  sucking.  In  the  normal  resting  position  they  ap- 
pear to  consist  of  a  long  jointed  proboscis,  blunt  at  the  tip,  with 

V 


Fig.  178.  Head  and  mouthparts  of  a  flea  (squirrel  flea,  Ceratophyllus  fasciatus) ; 
ant.,  antenna;  ant.  gr,,  antennal  groove;  cox.,  coxa  of  1st  leg;  cten.,  ctenidium; 
hyp.,  hypopharynx;  lab.  palp.,  labial  palpi,  which  together  form  a  tube  for  pro- 
tecting the  lancets;  mand.,  mandibles;  max.,  maxilla;  palp.,  maxillary  palpi; 
prothor.,  prothorax;  st.  pi.,  sternal  plate  of  skeleton  with  which  leg  is  articulated. 

a  pair  of  stout  triangular  flaps  at  either  side  at  the  base.  The 
triangular  parts  are  the  maxillae  and  each  is  provided  with  a 
stout  four-segmented  palpus,  which  might  easily  be  mistaken  for 
an  antenna.  The  proboscis  really  consists  of  a  pair  of  segmented 
gouge-shaped  structures,  the  labial  palpi,  which  fit  together  to 
form  a  more  or  less  perfect  tube,  in  which  lie  three  piercing 
organs.  The  latter  consist  of  a  pair  of  thin  bladelike  mandibles 
serrated  on  each  edge,  curved  at  the  tip,  and  provided  with  a 
longitudinal  groove,  and  a  single  bristle-like  organ,  the  epiphar- 
ynx.     In  piercing  the  skin  of  the  host  the  epipharynx  first  bores 


CLASSIFICATION 


407 


a  tiny  puncture,  and  then  the  serrated  mandibles  enlarge  the 
hole  by  an  up  and  down  sawing  motion.  As  these  organs  are 
sunk  into  the  flesh  of  the  host  the  labial  palpi  bend  back  like  a 
bow  under  the  flea's  head.  The  two  grooved  mandibles,  placed 
in  apposition,  form  a  tube  for  the  outflow  of  saliva,  while  the 
epipharynx,  which  is  also  grooved,  forms  a  tube  with  the  man- 
dibles for  the  inflow  of  blood.  The  digestive  tract  is  provided 
with  a  pharynx  which  acts  like  a  suction  pump,  and  a  very  large 
and  distensible  stomach. 

Classification.  —  Several  hundred  species  of  fleas  have  already 
been  described  and  it  is  probable  that  many  more  species  will  be 
found.  Although  some  authors  split  the  fleas  into  a  consider- 
able number  of  families,  it  is  more  usual  to  recognize  only  two 


Fig.  179.  Heads  of  common  fleas,  showing  distribution  of  ctenidia  or  "  combs"; 
A,  human  flea,  Pulex  irritans,  without  combs;  B,  dog  flea,  Ctenocephalus  canis, 
with  combs  on  both  head  and  pronotum ;  C,  rat  flea,  Ceratophyllus  fasciatus,  with 
only  pronotal  combs, 

well-defined  families  or  groups  —  the  Pulicidae  and  the  Sarcopsyl- 
lidse.  The  former  family  includes  all  the  "ordinary"  fleas,  whereas 
the  Sarcopsyllidae  is  a  very  specialized  group  of  fleas  with  a  much 
shortened  thorax,  which  appears  as  if  mashed  between  the  head 
and  abdomen,  with  slender  anterior  and  middle  legs,  and  with 
feeble  labial  palpi  of  only  three  segments.  Whereas  all  of  the 
Pulicidae  lay  their  eggs  singly,  or  in  small  groups,  and  develop- 
ment of  the  embryos  occurs  after  the  eggs  are  deposited,  in  some 
of  the  Sarcopsyllidae  the  eggs,  during  their  early  development, 
are  retained  in  the  abdomen  of  the  female,  which  swells  up  to 
such  a  size  that  the  head  and  thorax  appear  as  a  small  append- 
age at  one  end  of  it. 


408  FLEAS 

The  exact  identification  of  fleas,  especially  if  the  host  is  un- 
known, is  difficult,  being  based  largely  on  such  minute  charac- 
teristics as  relative  lengths  of  different  segments  of  the  legs, 
number  and  distribution  of  spines,  etc.  Most  species  of  fleas, 
however,  are  quite  closely  confined  to  their  respective  hosts,  only 
a  few  species  being  able  to  thrive  on  a  number  of  different  hosts. 
Some  of  the  commoner  species  of  the  fleas  which  are  of  most  im- 
portance to  man  can  be  fairly  closely  identified,  if  the  host  and 
geographic  locality  is  known,  by  the  presence  or  absence  of  the 
'^  combs  "  on  the  head  and  thorax.  The  common  human  flea, 
Pulex  irritans  (Fig.  179A),  and  the  Indian  rat  flea,  Xenopsylla 
cheopis  (Fig.  177),  have  no  combs,  the  common  rat  and  squirrel 
fleas  of  temperate  climates  (Figs.  179C  and  178)  have  only  the 
thoracic  comb,  while  the  cat  and  dog  fleas  (Fig.  179B)  have  both 
facial  and  thoracic  combs. 

Life  History  and  Habits.  —  The  life  history  of  all  fleas  is 
quite  similar.     Like  the  Diptera,  or  flies,  they  pass  through  a 

complete  metamorphosis, 
i.e.,  undergo  a  complete 
reorganization  from  larval 
to  adult  form  during  a 
resting  pupal  stage.     The 

Fig.  180.  Larva  of  Indian  rat  flea,  Xenop-  eggS  are  OVal,  whitish  in 
sytta^cheopis.      X  12.     (After  Bacot  and  Ride-    ^^^^^  ^^^  relatively  large, 

often  one-third  the  length 
of  the  parent  flea,  and  are  laid  singly,  except  in  the  chiggers, 
being  dropped  at  random  in  the  fur  of  the  host  or  in  the  lairs  or 
habitations  of  the  hosts.  The  human  flea,  for  instance,  lays  its 
eggs  in  the  dust  and  debris  in  cracks  in  floors,  under  carpets, 
etc.,  whereas  the  fleas  of  most  mammals  lay  their  eggs  loosely  in 
the  fur  of  the  host,  whence  they  drop  off  when  the  animal  shakes 
himself  or  prepares  to  sleep.  The  time  required  for  the  eggs  to 
reach  the  hatching  stage  varies  with  the  species  and  with  climatic 
conditions  from  two  or  three  days  to  over  two  weeks. 

The  larvae  (Fig.  180)  are  tiny  cyUndrical  maggot-like  creatures 
with  neither  legs  nor  eyes.  They  have  small  brown  heads  and 
whitish  bodies  composed  of.  13  segments,  which  are  provided  with 
rather  sparse  bristly  hairs  to  aid  in  crawhng.  The  last  segment 
is  terminated  by  a  pair  of  tiny  hooks. 

The  larvae  squirm  about  actively  in  the  dirt  or  debris  of  the 


LIFE  HISTORY  409 

lairs  or  rubbish  piles  in  which  they  hatched,  avoiding  light  and 
feeding  upon  what  bits  of  organic  matter  they  can  find,  such  as 
mouse  pills,  crumbs,  hairs,  epidermal  scales  from  their  hosts  and 
the  excrement  of  adult  fleas.  Some  species,  if  not  all,  devour  their 
shed  skins  after  moulting.  According  to  Bacot  and  Ridewood, 
who  have  recently  made  observations  on  the  larvae  of  a  number  of 
species  of  fleas,  the  larvae  become  very  excited  and  impatient 
when  disturbed.  They  sometimes  lie  quiet,  coiled  like  a  watch 
spring,  for  repose  or  concealment,  but  when  about  to  moult  they 
stretch  out  at  full  length.  They  crawl  by  alternately  expanding 
and  contracting  the  body  like  an  earthworm,  first  securing  a  hold 
with  the  hooks  at  the  posterior  tip  of  the  body,  then  with  the 
head  which  is  bent  under  to  hook  over  some  irregularity  on  the 
surface.  The  duration  of  the  larval  stage  varies  with  the  tem- 
perature and  humidity  and  to  some  extent  also  with  the  species. 
Under  favorable  conditions,  i.e.,  at  rela- 
tively low  temperatures  and  high  humid- 
ity and  with  plenty  of  food,  the  larvae  of 
some  species  pass  through  their  two 
moults  and  enter  the  pupal  stage  in  a 
week,  whereas  under  unfavorable  condi-  Fia.  I8i.  Cocoon  of 
tions  the  duration  of  the  larval  existence  ^  T2  ^  ^^'  ^  ^^  *^^ 
may  be  drawn  out  to  over  three  months. 

When  ready  to  undergo  their  transformation  into  adults,  the 
larvae  spin  little  silken  cocoons  which  are  somewhat  viscid,  so 
that  particles  of  dust  and  lint  readily  adhere  to  them  and  give 
them  a  dirty,  dingy  appearance  (Fig.  181).  According  to  Lyon 
the  adult  insects  may  emerge  from  the  cocoons  of  the  cat  flea, 
Ctenocephalus  felis,  in  from  two  to  14  days,  but  in  most  species 
at  least  a  week  is  required  for  the  transformation  to  take  place, 
and  this  time  may  be  greatly  increased  by  unfavorable  climatic 
conditions.  Strickland,  in  his  work  on  the  rat  flea  of  England, 
Ceratophyllus  fasdatus,  found  that  the  average  pupal  existence 
was  17  days  and  was  extended  to  four  months  or  more  by  low 
temperatures,  the  fully  formed  adult  insect  remaining  dormant 
within  the  cocoon  until  exposed  to  a  temperature  of  about  70°  F. 
There  is  much  probability  that  the  winter  in  temperate  climates 
and  the  hot  dry  season  in  tropical  climates  is  tided  over  by  fleas 
in  the  cocoon,  the  emergence  of  the  adults  coinciding  with  the 
advent  of  moderately  high  temperatures  and  humidity. 


410  FLEAS 

The  adult  fleas,  according  to  Strickland's  work  on  the  rat  flea, 
do  not  become  sexually  mature  for  some  days  after  they  escape 
from  the  cocoon,  and  copulation  does  not  occur  until  this  time, 
nor,  in  the  case  of  the  rat  flea,  until  after  a  feed  of  rat's  blood,  the 
latter  apparently  acting  as  a  stimulus  to  reproduction.  Soon 
after  copulation  the  eggs  begin  to  be  laid. 

In  the  dog  flea,  Ctenocephalus  canis,  the  entire  cycle  from  egg  to 
adult  is  said  to  be  passed  through  in  a  minimum  of  two  weeks,  in 
the  human  flea,  Pulex  irritans,  in  19  days  (in  southern  Europe) 
and  in  the  rat  fleas  in  about  three  weeks.  Ordinarily,  however, 
the  life  cycles  occupy  a  considerably  longer  time,  the  average 
being  from  one  to  three  months. 

The  length  of  life  of  adult  fleas  depends  largely  on  food  supply, 
temperature  and  humidity.  Unfed  fleas,  unless  allowed  to  bury 
themselves  in  rubbish,  usually  die  in  less  than  a  month,  though 
when  buried  in  debris  they  may  be  kept  alive  many  months. 
Well  fed  rat  fleas  kept  at  low  temperatures  (about  60°  F.)  and  high 
humidity  may  live  for  nearly  a  year  and  a  half,  according  to 
Strickland's  experiments.  The  optimum  climatic  conditions  and 
normal  length  of  life  probably  vary  a  great  deal  with  different 
species. 

Unlike  most  blood-sucking  insects,  fleas  usually  feed  at  fre- 
quent intervals,  usually  at  least  once  a  day,  and  sometimes  much 
oftener  than  this.  The  frequent  biting  is  due  to  the  fact  that 
fleas  are  very  easily  disturbed  while  feeding  and  seldom  complete 
a  meal  at  one  bite.  Moreover,  the  capacity  of  the  stomach  is 
not  so  great  as  in  many  other  blood-sucking  insects.  The  human 
flea  and  some  others  are  mainly  nocturnal,  visiting  their  hosts 
chiefly  at  night,  whereas  others,  such  as  the  cat  and  dog  fleas, 
remain  in  the  fur  of  the  host  nearly  all  the  time.  Some  species 
show  a  decided  preference  for  certain  parts  of  the  body  of  their 
host. 

Fleas  and  Disease.  —  Like  most  other  blood-sucking  parasites, 
fleas  are  intimately  connected  with  the  spread  of  disease.  The 
most  serious  charge  against  them  in  this  connection  is  the  dis- 
semination of  bubonic  plague,  which  as  a  human  scourge  ranks 
with  such  diseases  as  smallpox  and  leprosy.  In  fact,  few  diseases 
have  ever  ravaged  the  human  race  with  more  terrible  destruc- 
tiveness  than  plague  when  it  breaks  forth  as  an  epidemic  and 
becomes  rampant.     It  is  estimated  that  in  the  epidemic  of  the 


FLEAS  AND  PLAGUE  411 

14th  century  in  Europe  one-fourth  of  the  population  of  that 
continent,  or  25  miUion  people,  died  of  the  disease.  Superstition 
and  unreasoning  terror  led  to  horrible  persecution  and  torture  of 
innocent  people  who  were  supposed  to  cause  the  plague.  At 
present  the  disease  is  practically  confined  to  tropical  countries, 
and  is  especially  prevalent  in  India,  where  an  average  of  about  one 
million  deaths  a  year  are  caused  by  it.  The  practical  disappear- 
ance of  plague  from  Europe  is  thought  by  some  authors  to  be 
associated  with  a  change  in  the  rat  fauna  of  Europe,  the  do- 
mestic and  gregarious  black  rat,  Epimys  rattus,  being  replaced 
by  the  wilder  and  more  scattered  brown  rat,  Epimys  norvegicus. 
The  disease,  however,  has  often  been  introduced  from  the  tropics 
into  other  countries,  and  there  is  constant  danger  of  this  wherever 
the  strictest  preventive  regulations  are  not  enforced.  In  1900 
the  disease  was  introduced  into  San  Francisco,  and  there  is  every 
reason  to  believe  that  had  knowledge  of  preventive  medicine 
been  at  the  point  where  it  was  300  years  ago,  the  United  States 
would  have  been  swept  as  was  Europe  in  the  14th  century.  In- 
stead, knowing  that  rats  were  the  chief  reservoir  of  the  disease, 
and  that  rat  fleas  were  instrumental  in  transmitting  the  disease 
from  rat  to  man,  the  U.  S.  Public  Health  Service  took  hold  of  the 
situation  and  instituted  an  anti-rat  campaign  such  as  had  never 
been  thought  of  before.  Over  a  million  rats  were  caught,  ex- 
amined and  destroyed  in  the  city  of  San  Francisco.  The  infec- 
tion spread,  however,  and  became  established  in  the  ground 
squirrels  of  several  counties  in  California.  From  July  1,  1913,  to 
November,  1914,  over  20,000,000  ground  squirrels  were  destroyed 
in  infected  districts  in  California.  So  strenuous  were  the  efforts 
to  stamp  out  the  disease  before  it  could  get  beyond  control  that 
only  187  cases  of  the  disease  in  man  occurred  in  California, 
with  none  since  1914.  New  Orleans  has  also  had  a  taste  of  plague, 
and  infected  rats  have  been  taken  in  the  vicinity  of  the  water 
front  in  Seattle. 

The  steps  which  have  made  possible  an  intelligent  fight  against 
plague  were  the  discovery  of  the  plague  germ.  Bacillus  pestis, 
by  Yerson  in  1894,  the  establishment  of  the  identity  of  the  disease 
with  that  of  rats  by  the  same  worker,  the  discovery  of  the  mul- 
tiplication of  the  plague  germs  in  the  gut  of  rat  fleas,  Xeno- 
psylla  cheopis,  by  Liston  in  1905,  and  finally  conclusive  experi- 
mental proof  by  the  British  Plague  Commission  in  India  in 


412  FLEAS 

1906  that  the  rat  flea  was  the  principal  means  of  transmission  of 
the  bubonic  form  of  the  disease. 

As  far  as  is  known  the  plague  bacilli  live  only  in  the  digestive 
tract  of  the  fleas  and  do  not  infect  either  the  saliva  or  the  body 
cavity.  From  this  fact  it  is  evident  that  the  germs  are  inoculated 
into  the  wound  made  by  the  flea,  either  with  the  excrement  which 
is  commonly  voided  while  sucking  blood  or  with  regurgitated 
blood.  It  has  been  pointed  out  that  a  rat  flea's  stomach  will 
hold  about  one-half  a  cubic  centimeter  of  blood  and  could  there- 
fore take  5000  germs  with  a  single  feed  from  an  infected  animal. 
These  often  multiply  to  such  an  extent  as  to  form  a  solid  mass  of 
organisms,  blocking  the  digestive  tract  of  the  insect  (Fig.  182). 
It  has  been  stated  that  when  the  stomach  and 
intestine  of  a  flea  are  plugged  with  plague 
germs  the  normal  action  of  the  valves  of  the 
digestive  tract  is  lost,  and  the  pumping  move- 
ments of  the  pharynx  result  in  regurgitating 
infected  material  into  the  wound  instead  of 
sucking  fresh  blood  from  it.  Fleas  were  found 
by  the  British  Plague  Commission  to  remain 
infective  for  15  days  during  the  height  of  an 
_.        epidemic,    though    during    the    non-epidemic 

Fig.    182.     Diges-      ^  •j.-ji  -j-rx-  r 

tive   tract    of    flea  season    no   mdividual    remamed    mfective    tor 
plugged   with    solid  ^QYQ  ^]^an   seven   days.     In  Java  the  Indian 

growth  (in  black)  of  ■       •    t-      .- 

plague  bacilli.  (After  rat  fleas  have  been  found  to  remain  infective 
Manson.)  fQj.  33  days  and  Bacot  has  found  the  European 

rat  flea,  Ceratophyllus  fasciatus,  to  remain  infective,  when  kept 
away  from  a  host,  for  47  days. 

The  Indian  rat  flea,  Xenopsylla  cheopis  (Fig.  177),  is  the  species 
most  intimately  associated  with  plague  transmission.  This  spe- 
cies has  been  introduced  with  rats  on  ships  into  all  parts  of  the 
tropics,  and  into  seaports  in  many  temperate  countries,  especially 
such  ports  as  San  Francisco,  which  trade  extensively  with  the 
Orient.  This  species,  however,  is  by  no  means  the  only  one 
which  can  serve  in  the  transmission  of  plague.  It  is  probable 
that  any  species  which  will  attack  both  man  and  other  sus- 
ceptible animals,  such  as  rats  and  ground  squirrels,  may  transmit 
the  infection.  Thus  in  India  the  human  flea,  Pulex  irritans, 
and  the  European  rat  flea,  Ceratophyllus  fasciatus,  have  been 
proved  experimentally  to  be  plague  carriers,  and  in  California 


DISEASES  TRANSMITTED  BY  FLEAS  413 

the  squirrel  fleas,  Hoplopsyllus  anomalus  and  Ceratophyllus  acutus, 
also  have  been  shown  to  carry  the  infection.  It  is  evident  also 
that  other  animals  besides  rats  and  man  are  susceptible  to  the 
disease.  Ground  squirrels,  Citellus  beecheyi,  guinea-pigs  and 
monkeys  have  been  shown  to  be  susceptible.  A  marmot  or 
ground  hog,  Arctomys  hobac,  common  in  Manchuria,  is  thought 
to  have  been  the  chief  reservoir  of  the  disease  in  the  Manchurian 
epidemic  in  the  winter  of  1910-11,  the  flea  Ceratophyllus  silan- 
tiewi  being  the  transmitting  agent. 

Doubtless  any  fleas  which  attack  these  animals  and  which 
also  attack  man  may  be  instrumental  in  spreading  the  plague  to 
human  beings  in  direct  proportion  to  the  willingness  with  which 
they  will  bite  man,  and  to  their  opportunities  for  doing  so.  It 
must  not  be  inferred  that  only  fleas  can  transmit  the  disease. 
The  pneumonic  form  of  plague,  which  is  relatively  uncommon, 
is  transmitted  by  particles  of  sputum  or  mucus  from  the  mouth  or 
lungs.  The  bubonic  plague  may  also  be  transmitted  by  bedbugs 
and  perhaps  by  other  parasitic  insects.  A  head  louse  taken  from 
a  plague  patient  was  found  to  be  infected.  There  can  be  no 
doubt,  however,  that  the  rat  fleas  are  by  far  the  most  important 
spreaders  of  this  terrible  disease. 

A  similar  but  milder  disease  of  rodents,  transmissible  to  man, 
occurs  in  western  United  States.  It  is  caused  by  Bacterium 
tularense  and  is  known  as  tularemia.  Deerflies  and  certain  lice 
have  been  shown  to  be  transmitting  agents,  but  the  role  of  fleas 
is  only  conjectured. 

Another  disease  which  is  commonly  believed  to  be  transmitted 
by  fleas  is  the  Mediterranean  or  infantile  form  of  kala-azar 
(see  p.  83).  This  is  prevalent  in  dogs  throughout  many  of  the 
regions  bordering  the  Mediterranean,  especially  in  parts  of  Italy 
and  North  Africa,  and  is  the  cause  of  a  high  mortality  in  the 
numerous  cases  which  occur  among  children.  A  number  of 
authors  have  carried  on  experiments  to  prove  the  instrumentality 
of  the  common  dog  flea,  Ctenocephalus  canis,  and  also  of  the 
human  flea,  Pulex  irritans,  with  varied  results.  (See  Chap.  V, 
p.  83.)  The  role  of  fleas  in  the  transmission  of  this  disease  is 
still  uncertain  but  there  is  enough  evidence  against  the  fleas  to 
warrant  their  being  looked  upon  with  extreme  suspicion  until 
definitely  proved  innocent. 

Another  instance  of  the  instrumentality  of  fleas  in  the  trans- 


414  FLEAS 

mission  of  disease  is  their  relation  to  the  spread  of  certain  species 
of  tapeworms,  especially  the  common  dog  tapeworm,  Dipylidium 
caninum.  The  larval  stage  of  this  tapeworm  is  passed  in  the  body 
cavity  of  the  dog  flea,  Ctenocephalus  canis,  the  eggs  of  the  parasite, 
adhering  to  hair  in  the  vicinity  of  the  anus,  being  ingested  by  the 
flea.  Occasional  infection  of  human  beings,  especially  young 
children,  occurs  by  the  accidental  swallowing  of  infected  fleas,  a 
thing  which  could  easily  happen  in  cases  of  too  great  intimacy  be- 
tween children  and  their  pet  dogs.  As  many  as  50  larvae  of  Dipy- 
lidium  have  been  found  in  a  single  flea.  The  larvae  can  also  de- 
velop in  the  human  flea.  The  rat  flea,  Xenopsylla  cheopis,  has 
been  found  to  harbor  the  larval  stages  of  tapeworms  of  the  genus 
Hymenolepis,  as  many  as  nine  cysticercoids  having  been  found 
in  a  single  specimen.  These  tapeworms  are  normally  parasitic  in 
rats  and  mice  but  occasionally  parasitize  man  also. 

The  relation  of  fleas  to  other  diseases  is  suspected.  A  German 
writer  has  put  forth  the  theory  that  fleas  are  instrumental  in 
the  transmission  of  typhus.  If  typhus  is  purely  a  bacterial 
disease,  its  spread  by  fleas  and  other  parasites  as  well  as  by  lice 
would  be  quite  possible,  but  if  it  should  be  found  to  be  caused  by 
an  organism  which  requires  a  true  intermediate  host,  it  would 
be  doubtful  whether  such  widely  different  insects  as  lice  and 
fleas  could  both  function  in  the  same  manner.  That  fleas 
might  act  as  mechanical  transmitters  of  such  diseases  as  tuber- 
culosis and  syphilis  is  quite  possible,  though  it  is  doubtful  if 
this  often  occurs. 

Important  Species 

Human  Flea.  —  The  only  species  of  flea  which  is  known  to  be 
a  parasite  of  man  primarily,  with  the  exception  of  the  chigger, 
is  the  appropriately  named  human  flea,  Pulex  irritans,  though 
in  many  places  man  is  annoyed  more  by  certain  other  species 
which  are  primarily  parasites  of  his  domestic  animals.  The 
human  flea  is  not  exclusively  a  parasite  of  man.  It  also  attacks 
badgers,  skunks,  dogs  and  other  carnivores,  occasionally  occurs 
on  rats  and  mice,  especially  in  houses  and  ships,  and  has  been 
taken  on  the  blacktail  deer,  Odocoileus  columhianus}     It  is  now 

1  Specimens  of  fleas  taken  in  considerable  numbers  on  deer  in  northern 
California  by  F.  C.  Clarke,  of  the  California  Fish  and  Game  Commission, 
were  identified  by  Prof.  R.  W.  Doane  of  Stanford  University  as  Pulex  irritans. 
On  account  of  the  distinctive  habits  of  these  deer  fleas,  Clarke  (in  Htt.) 
believes  that  they  should  be  considered  a  variety  of  P.  irritanSy  for  which  he 
proposes  the  name  P.  irritans  cervi. 


HUMAN  FLEA  415 

cosmopolitan  in  distribution,  probably  having  originated  in 
Europe,  whence  it  was  introduced  with  Europeans  to  all  parts 
of  the  world.  This  flea  is  the  species  which  has  made  California 
as  famous  for  its  fleas  as  is  New  Jersey  for  its  mosquitoes.  The 
relatively  cool  humid  summer  climate  combined  with  a  mild 
wet  winter  make  the  Pacific  Coast  of  the  United  States  an  ideal 
place  for  this  pest.  Though  more  or  less  of  a  nuisance  through- 
out the  year  in  mild  cHmates,  this  flea  is  less  troublesome  in 
winter,  due  to  relative  inactivity,  to  slower  reproduction,  and 
to  the  fact  that  small  mammals  are  more  commonly  attacked  at 
this  time  of  year. 

The  human  flea  is  readily  distinguished  from  most  common 
species  in  temperate  climates  by  the  absence  of  any  combs, 
either  on  the  head  or  thorax.  From  the  Indian  rat  flea,  Xeno- 
psylla  cheopis  (Fig.  177),  it  is  diflSicult  to  distinguish,  the  essential 
difference  being  the  presence  in  the  rat  flea  and  absence  in  the 
himian  flea  of  a  vertical  chitinous  thickening  of  the  mesoster- 
num,  i.e.,  the  plate  to  which  the  middle  leg  is  artiijulated  on 
either  side.  The  antennae  of  the  human  flea  are  shorter  and 
more  knoblike  than  are  those  of  Xenopsylla. 

The  human  flea  secretes  itself  in  crevices  and  cracks  of  houses, 
in  floors,  rugs,  bedding,  etc.,  coming  forth  chiefly  at  night  to 
pierce  the  flesh  and  suck  the  blood  of  its  hosts.  The  suscep- 
tibility of  different  individuals  to  flea  bites  is  variable.  The 
irritation  that  is  normally  produced,  probably  chiefly  as  a  result 
of  the  injection  of  the  insect's  salivary  secretions  into  the  wound, 
causes  the  formation  of  a  reddish  pimple  with  more  or  less  swell- 
ing. Some  people,  however,  are  apparently  entirely  immune  to 
flea  bites  and  feel  no  pain  from  them.  The  writer  is  one  of  these 
fortunate  individuals.  On  his  first  visit  to  California  he  had 
been  fully  warned  concerning  the  ravages  of  the  fleas  but  found  to 
his  pleasant  surprise  that  the  only  discomfort  felt  from  fleas  was 
the  tickling  occasionally  caused  by  their  movements  beneath 
his  clothing.  A  college  roommate,  however,  was  attacked  to 
such  an  extent  as  to  be  unable  to  sleep,  and  spent  a  considerable 
part  of  many  nights  in  pursuit  of  the  wily  fleas  and  in  violent 
massaging  of  painful  wounds. 

As  has  been  noted,  the  human  flea  may  act  as  a  transmitter 
of  plague,  infantile  kala-azar  and  tapeworm  {Dipylidium)  in- 
fection, though  it  is  not  the  chief  villain  in  the  spread  of  any  one 
of  these  diseases. 


416  FLEAS 

Dog  and  Cat  Fleas.  —  Next  in  importance  to  the  human  flea 
as  a  parasite  of  man  is  the  dog  flea,  Ctenocephalus  canis,  and  the 
closely  alUed  cat  flea,  C.  felis.  In  the  southeastern  United  States 
where  the  flea  scourge  is  as  great  if  not  greater  than  in  Cali- 
fornia, the  dog  flea  is  the  species  usually  met  with.  During  the 
moist  hot  summers  this  species  becomes  exceedingly  abundant. 
Although  primarily  a  parasite  of  dogs  this  flea  wilhngly  includes 
man  in  its  bill  of  fare  if  opportunity  offers,  and  also  attacks 
cats,  rats  and  other  mammals.  The  usual  fleas  of  cats,  how- 
ever, are  now  generally  considered  to  be  specifically  distinct  from 
the  dog  flea.  The  cat  flea  is  the  only  one  of  the  two  species 
found  in  India,  where  it  is  a  common  parasite  of  dogs  as  well 
as  cats.  The  cat  flea  has  a  longer  and  more  slender  head  than 
its  near  relative.  Both  species  can  readily  be  distinguished 
from  any  other  common  species  with  similar  habits  by  the  pres- 
ence of  two  conspicuous  combs,  one  along  the  ventral  margin  of 
the  head,  the  other  on  the  pronotum  (Fig.  179B). 

The  eggs  of  dog  and  cat  fleas  are  usually  laid  loosely  in  the  fur 
of  their  host,  whence  they  readily  fall  out  when  the  host  shakes 
himself  or  is  settling  himself  for  a  nap.  They  develop  in  the 
dust  and  dirt  of  kennels,  woodsheds,  house  floors  or  other  places 
where  infested  animals  are  likely  to  go.  Houses,  of  course,  be- 
come infested  through  the  agency  of  infested  animals,  and  since 
the  fleas,  once  in  houses,  encounter  man  more  readily  than  they 
do  the  original  hosts,  man  is  very  likely  to  suffer  from  their  at- 
tacks. Patton  and  Cragg  found  the  inside  of  a  hat,  in  which  a 
kitten  had  slept  overnight,  so  full  of  flea  eggs  that  it  looked  as  if 
it  had  had  sugar  sprinkled  in  it  from  a  sifter.  Another  author 
collected  a  teaspoonful  of  eggs  from  the  dress  of  a  lady  who  had 
held  a  kitten  in  her  lap  for  a  short  time.  The  writer  has  been 
able  to  flnd  a  similar  quantity  of  eggs  by  dusting  a  smooth  hard- 
wood floor  after  an  infested  dog  had  indulged  in  one  vigorous 
shake.  With  these  instances  in  mind  one  can  readily  understand 
how  houses  into  which  infested  pets  are  admitted  become  over- 
run with  fleas. 

The  dog  flea,  from  its  habits,  is  the  species  most  frequently 
imphcated  in  the  transmission  of  kala-azar  (see  p.  83),  and  is 
the  species  usually  instrumental  in  transmitting  tapeworm 
{Dipylidium)  infection  to  children.  Since  this  species  will  feed 
on  rats  there  is  no  reason  for  doubting  that  it  may  act  as  a  trans- 


RAT  AND  SQUIRREL  FLEAS  417 

mitter  of  bubonic  plague,  though  its  preference  for  dogs  or  cats 
would  preclude  a  frequent  occurrence  of  this. 

Rat  and  Squirrel  Fleas.  —  The  various  species  of  rat  and  squir- 
rel fleas  are  only  accidental  parasites  of  man.  They  readily  at- 
tack him  if  opportunity  offers  but  do  not  remain  adherent  to  him 
as  they  do  to  their  normal  hosts.  If  it  were  not  for  their  enormous 
importance  in  the  spread  of  bubonic  plague,  they  would  hardly 
need  special  consideration. 

From  its  intimate  connection  with  the  spread  of  bubonic 
plague,  the  Indian  rat  flea,  Xenopsijlla  cheopis  (Fig.  177),  is  of 
prime  importance.  Though  other  members  of  the  genus  are 
confined  to  Africa  and  Asia,  this  species  has  now  a  world-wide 
distribution,  having  accompanied  its  normal  host,  the  rat,  to  all 
warm  seaports  in  both  the  Old  and  the  New  World.  It  is  a 
rather  short,  stout  flea,  resembling  the  human  flea  in  the  absence 
of  combs.  Although  the  normal  hosts  of  Xenopsylla  cheopis  are 
rats  of  various  species,  the  domestic  habits  of  these  rodents 
bring  the  fleas  into  close  association  with  man,  and  they  will 
readily  feed  upon  him  if  hungry.  Furthermore,  deRaadt  has 
recently  demonstrated  that  these  fleas  do  not  remain  constantly 
in  the  fur  of  their  normal  hosts,  but  that  80  per  cent  drop  off  in 
the  course  of  48  hours.  This  species  is  not  migratory  and  sel- 
dom reaches  anyone  but  the  inhabitants  of  the  house  in  which  its 
host  occurs,  unless  carried  by  the  rats  themselves.  Swellen- 
grebel  states  that  in  Java  this  flea  will  wiUingly  bite  man  on  the 
first  day  of  fasting.  In  many  tropical  countries  the  Indian  rat 
flea  is  the  commonest  flea  found  in  houses;  in  Egypt  96  per  cent 
of  fleas  caught  in  plague-infested  houses  were  of  this  species. 

The  European  rat  flea,  Ceratophyllus  fasciatus,  is  a  species 
having  habits  quite  similar  to  those  of  Xenopsylla  cheopis.  It 
replaces  the  latter  species  in  temperate  climates  except  in  sea- 
ports, where  the  Indian  rat  flea  is  often  more  common.  The 
common  rat  flea  of  China  and  Japan  is  Pygiopsylla  ahalce.  The 
larvae  of  C.  fasciatus  develop  best  under  cool  humid  conditions 
in  an  abundance  of  rubbish.  Strickland,  who  has  worked  out 
the  biology  of  this  flea  in  detail,  found  that  it  would  actually 
attack  man  in  preference  to  rats,  although  a  feed  on  the  blood  of 
rats  seemed  to  be  necessary  before  any  eggs  were  laid.  Another 
species  of  the  same  genus,  C.  gallinoB,  attacks  chickens  in  Europe, 
and  has  been  introduced  into  several  parts  of  the  United  States. 


418  FLEAS 

It  is  said  to  be  very  annoying  to  man  also.  The  common  squir- 
rel flea  in  North  America,  C.  acutus,  is  found  on  a  number  of 
species  of  wild  rodents,  and  also  occasionally  on  rats  and  mice. 
It  does  not  attack  man  so  readily  as  does  C.  fasciatus,  but  is 
nevertheless  not  averse  to  human  blood.  This  species  has 
come  into  great  importance  in  California  as  the  transmitter  of 
plague  from  rats  to  ground  squirrels.  It  is  probable,  how- 
ever, that  other  species  of  this  genus  and  of  allied  genera 
may  quite  as  readily  transmit  plague,  depending  only  on  the 
extent  to  which  their  habits  bring  them  in  contact  with  infected 
animals. 

Chiggers.  —  The  chigger,  chigoe,  jigger  or  sand  flea,  Derma- 
tophilus  (or  Rhynchoprion)  penetrans  (Fig.  183),  as  it  is  vari- 
ously called,  is  one  of  the  most  de- 
spised pests  of  tropical  countries. 
It  is  a  very  small  flea  of  the  family 
SarcopsylUdse,  about  one  mm.  in 
length,  with  no  comblike  spines 
and  relatively  slender  legs.  It  has 
a  very  comical  pointed  forehead, 
like  a  helmet  worn  with  the  point 
forward.  The  males  and  virgin 
females  of  this  species  are  similar 

Fig.   183.     Chigger  or  burrowing    ,         ,^         n  '      i     ^  -,  ^   ji     j 

flea,    Dermatophilus    penetrans,    un-    ^0  O^^^r  fleaS  m  hablts,  eXCept  that 

impregated   female.    X  30.    (After  they  attack  a  wide  range  of  hosts. 

Karsten  from  Riley  and  Johannsen.)    -,/r         ■      ,^  •      •      i    i       j       n    ,^  • 

Man  IS  the  prmcipal  host  of  this 
particular  species,  but  pigs  are  also  very  commonly  attacked. 
Chiggers  occur  especially  in  sandy  regions  where  there  is  much 
underbrush,  and  here  they  lie  in  ambush  on  the  vegetation,  dead 
leaves  or  sandy  soil,  ready  to  attack  any  host  which  may  come 
their  way.  The  particular  importance  of  this  flea  lies  in  the 
fact  that  the  impregnated  females  have  the  aggravating  habit 
of  burrowing  into  the  skin  especially  in  such  tender  spots  as  under 
the  toe  nails,  where,  nourished  by  the  blood  of  the  host,  the  eggs 
develop  and  cause  the  abdomen  to  swell  into  a  great  round  ball 
as  large  as  a  pea,  leaving  the  head  and  legs  as  inconspicuous 
appendages  (Fig.  184).  Only  the  two  posterior  segments  of  the 
abdomen  do  not  enlarge;  these  act  as  a  plug  for  the  hole  made  in 
entering  the  skin.  The  eggs,  up  to  a  hundred  in  number,  mature 
in  about  a  week  and  are  then  expelled  by  the  female  through  the 


CHIGGER 


419 


Chigger  or  burrowing  flea,  Der- 
X  18. 


protruding  end  of  the  abdomen.     Sometimes  the  entire  female 

is  expelled  with  her  eggs  by  the  pressure  of  the  inflamed  tissue 

which  surrounds  her.    The 

eggs,    which    fall    to    the 

ground,    soon    hatch    into 

typical  flea  larvae  (Fig.  185). 

These,  if  they   happen  to 

fall    on    sandy    soil    under 

conditions    suitable    for 

their    development,     grow 

to  maturity,  pupate  in   a 

cocoon  and  emerge  as  adult 

insects  in  the  course  of  ten 

days  or  two  weeks.  fig.  184. 

The  wounds  made  by  the    ^^f^^ophilus    penetrans,    gravid    female 
,    .       ,        ,  .       (After  Moniez.) 

burrowmg  female  in  the  skm 

become  much  inflamed  and  very  painful.  Frequently  the  dis- 
tended abdomen  of  a  flea  is  crushed  and  the  eggs  released  in  the 
wound.  In  such  cases  the  inflammation  is  greatly  increased  un- 
less the  crushed  body  and  eggs  are  immediately  expelled.  As 
soon  as  the  eggs  are  laid,  or  even  before,  the  skin  surrounding  the 
wound  ulcerates  and  pus  is  formed.  The  empty  female  flea  is  ex- 
pelled. The  sore  which  is  left 
is  very  liable  to  infection  by  bac- 
teria and  frequently  results  in 
the  loss  of  toes  or  even  whole 
limbs  through  blood-poisoning. 
Quiros  has  recently  pointed  out 
that  in  Central  America,  where  chigger  infection  is  very  common, 
especially  in  boys  who  play  barefooted  in  the  streets  along  which 
infected  hogs  are  driven  to  public  market,  deaths  from  tetanus 
and  gas  gangrene  from  chigger  wounds  are  very  common. 

Although  usually  only  a  few  chiggers  are  present  at  a  time, 
there  are  cases  where  hundreds  infest  a  person  at  once,  literally 
honeycombing  the  skin  and  making  the  feet  or  other  parts  of 
the  body  so  sore  that  the  victim  is  rendered  a  complete  invalid. 
This  obnoxious  flea  formerly  existed  only  in  the  tropical  por- 
tions of  America,  especially  in  the  West  Indies,  but  it  was  intro- 
duced to  the  West  Coast  of  Africa  in  1872,  and  has  since  become 
abundant  throughout  the  tropical  parts  of  that  continent  and 


Fig.  185.     Larva  of  chigger,  Dermatoph 
ilus  penetrans.     (After  Newstead.) 


420  FLEAS 

in  the  neighboring  islands.  It  has  also  been  introduced  by  coolies 
into  India,  but  does  not  seem  to  thrive  there  as  it  does  in  tropical 
America  and  Africa. 

The  treatment  of  chigger  wounds  formerly  consisted  in  the 
destruction  of  the  fieas  while  imbedded  in  the  wounds.  This  was 
done  by  applying  various  insecticides  or  pricking  with  a  needle, 
the  dead  insect  being  removed  after  ulceration.  A  much  better 
method  is  to  enlarge  the  entrance  hole  of  the  flea  with  a  clean 
needle  and  remove  the  parasite  entire.  The  wound  should  then 
be  carefully  dressed  and  protected  until  healed.  An  ointment 
recommended  by  Quiros  consists  of  23^  grams  salicylic  acid  and 
10  grams  ichthyol  in  10  grams  of  yellow  vaseline.  Bathing  of 
infected  parts  with  kerosene  oil  is  also  recommended. 

Chiggers  can  be  avoided  to  a  large  extent  by  the  use  of  high 
boots,  or  shoes  and  leggings.  Walking  barefooted  in  chigger- 
infested  regions  is  almost  sure  to  result  in  attacks  by  these  pests. 
Houses,  yards,  etc.,  in  chigger  regions  should  be  kept  carefully 
clean  of  dust,  dirt  and  debris  which  might  favor  the  develop- 
ment of  the  parasites.  In  Central  America  Quiros  recommends, 
as  one  of  the  best  preventive  measures,  a  prohibition  against 
driving  hogs  affected  with  chiggers  through  the  streets,  along 
with  regulations  for  treating  affected  hogs  where  they  are  raised. 
According  to  Penschke,  in  German  East  Africa,  attacks  by  chig- 
gers can  be  prevented  by  thoroughly  rubbing  the  feet  every  two 
or  three  days  with  vaseline  to  which  has  been  added  a  few  drops 
of  lysol  or  cresol  soap  (15  drops  to  3 J  oz.  of  vaseline). 

Sticktight  Flea.  —  The  "  sticktight  "  flea,  Echidnophaga  galli- 
nacea  (Fig.  186),  is  another  member  of  the  family  Sarcopsyllidse 
which  may  be  a  human  pest.  It  is  a  small  dark-colored  flea  which 
very  commonly  attacks  chickens  in  nearly  all  tropical  and  sub- 
tropical countries,  including  the  southern  United  States  in 
America.  Although  the  normal  host  is  the  chicken,  other  poultry, 
dogs,  cats,  domestic  rabbits,  rats  and  other  animals,  as  well  as 
man,  are  attacked.  This  species  gets  its  name  from  the  tenacity 
with  which  it  adheres  to  its  host.  It  is  gregarious,  collecting  in 
dense  masses  on  the  heads  of  poultry  (Fig.  186),  in  the  ears  of 
mammals  and  in  other  places.  It  is  not  averse  to  attacking 
man,  especially  children,  but  since  it  is  not  so  active  as  other 
fleas  it  can  easily  be  found  and  removed.  No  disease  is  known  to 
be  transmitted  by  this  flea. 


PREVENTION  421 

Prevention.  —  Strict  cleanliness  in  private  homes  or  public 
buildings  prevents  fleas  from  breeding  in  them.  Uncared-for 
carpets  and  straw  mattings  afford  excellent  breeding  grounds 
for  the  human  flea,  as  do  dusty  cracks 
between  floor  boards,  unswept  corners 
under  sinks,  and  any  other  place  where 
the  eggs  and  young,  undisturbed,  may 
obtain  enough  moisture  to  keep  them 
from  drying  up.  The  use  of  bare  hard- 
wood floors  with  rugs  which  can  readily 
be  taken  up  and  swept  and  thorough 
sweeping  in  corners  and  under  pieces 
of  furniture,  sinks,  etc.,  do  not  give 
fleas  an  opportunity  to  breed  in  the  ^^\^\^ 
home  or  in  pubHc  buildings,  and  are  pj^^  igg.  Head  of  chicken 
therefore  valuable  preventive  measures,   infested    with    chicken    flea, 

Oj.  ,,       r      J.  r     -jj-  Echidnophaga      gallinacea. 

ne  of  the  best  means  ot  riddmg  an   (^fter  Bishopp.) 

infested   house   of   fleas  is  to  sprinkle 

the  floors  with  naphthaline  and  close  the  rooms  for  a  day  or 
two.  This  will  effectually  kill  all  adult  and  larval  fleas,  and  the 
eggs  may  then  be  destroyed  by  washing  the  floors  with  hot  soap- 
suds, a  five  per  cent  formalin  solution  or  one-tenth  per  cent 
solution  of  corrosive  sublimate.  It  is  claimed  that  alum  swept 
into  carpets  or  a  solution  of  alum  soaked  into  carpet  paper  pre- 
vents fleas  from  breeding. 

Fleas  are  very  susceptible  to  fumigation  with  hydrocyanic 
acid  gas.  Experiments  by  the  U.  S.  Public  Health  Service  show 
that  fleas  succumb  to  the  amount  of  gas  generated  by  two  and 
one-half  ounces  of  potassium  cyanide  in  1000  cubic  feet  of  space. 
Fumigation  with  sulphur  is  also  effective.  Details  of  methods 
of  fumigation  with  these  substances  will  be  found  on  p.  383. 
Sodium  fluoride  in  the  form  of  a  crystalline  powder  scattered 
on  floors  or  blown  about  by  means  of  a  dust-gun  will  probably 
prove  effective  against  fleas,  as  it  has  against  cockroaches 
and  other  insects.  It  is  inexpensive  and  not  dangerous  to 
handle. 

Various  traps  for  the  capture  of  adult  fleas  have  been  devised, 
one  of  the  simplest  and  most  effective  being  to  clothe  the  legs  in 
sticky  fly  paper,  and  wander  about  in  the  infested  rooms.  A 
badly  infested  building  in  Cornell  University  was  cleared  of  fleas 


422 


FLEAS 


in  this  manner.  Another  device,  used  by  the  Chinese,  is  a  rod 
of  bamboo,  smeared  with  bird  Hme,  fitted  inside  of  a  larger  piece 
of  bamboo  which  has  holes  cut  in  it.  A  trap 
of  similar  type  may  be  constructed  by  fitting  a 
piece  of  broomstick  wrapped  with  sticky  fly 
paper  inside  a  wire  cylinder  (Fig.  187).  Such 
a  ''  flea  stick  "  can  be  roUed  about  on  floors  or 
in  beds  and  will  collect  a  large  proportion  of 
the  flea  population.  Another  trap  consists  of 
a  glass  of  water  with  about  an  inch  of  oil  on 
the  top  of  it  fitted  with  a  little  wick  in  the 
center  of  a  floating  piece  of  cork.  This  is 
placed  in  the  center  of  a  dish  of  strong  soap- 
suds and  lighted  at  night.  The  light  attracts 
the  fleas,  which  leap  headlong  into  the  soap- 
suds. 

The  destruction  of  fleas,  especially  cat  and 
dog  fleas,  on  domestic  animals  is  often  neces- 
sary in  order  to  do  away  with  a  flea  scourge. 
Dogs  and  cats,  or  other  hosts,  may  be  cleared 
of  fleas  by  washing  them  in  two  or  three  per 
broomstick  wrapped  cent  solution  of  creolin  (about  one  tablespoon- 

with  sticky  fly  paper,    p    -i    ,  xr  x\  a.T_ 

fitted  in  a  cylinder  ^  to  a  quart  of  Warm  water),  or  some  other 
derivative  of  creosote,  or  a  similar  solution  of 
potassium  sulphide.  According  to  Bishopp, 
the  solution  should  be  worked  into  the  hair  with  a  brush, 
and  care  should  be  taken  to  wet  the  fleas  which  crowd 
toward  the  head  of  the  animal.  After  about  ten  minutes 
the  solution  should  be  washed  off  with  warm  water  and  soap, 
at  least  in  delicate-skinned  animals  such  as  cats,  to  avoid  a 
burning  effect.  Another  method  of  treatment  is  to  rub 
powdered  moth-balls  (naphthaline)  into  the  fur.  This  causes 
the  fleas  to  emerge  from  the  fur  in  a  stupefied  condition  in 
which  they  are  easily  captured  and  destroyed.  Except  to  sicken 
cats  slightly  for  a  day  or  two  this  treatment  has  no  ill  effect 
on  the  host. 

Of  temporary  value  in  flea-infested  places  is  the  use  of  repel- 
lents, such  as  oil  of  pennyroyal,  eucalyptus  oil,  etc.,  smeared  on 
shoes  or  clothing,  or  between  bed  sheets.  Beds  may  be  isolated 
by  elevating  them  to  some  distance  from  the  floor,  or  by  sur- 


FiG.  187.  A 
modification  of  the 
Chinese  flea  trap. 
Constructed      of      a 


of  wide-meshed  wire 
net.  (After  Bishopp.) 


REPELLENTS  423 

rounding  them  with  a  band  of  sticky  fly  paper  12  to  14  inches 
wide.  Where  perfect  protection  from  fleas  is  desired,  as  in  a 
plague-smitten  city,  all  of  these  protective  measures,  as  well  as 
fly-paper  wrapped  legs,  and  any  other  means  which  may  come  to 
mind  should  be  made  use  of.  These  should  be  followed  up  by 
the  more  permanent  measures  leading  to  the  extermination  of 
both  larval  and  adult  fleas. 


CHAPTER  XXV 

MOSQUITOES 

Importance.  —  Of  all  existing  insect  pests  mosquitoes  are  the 
greatest  enemies  of  mankind.  The  mere  annoyance  which  the 
enormous  numbers  of  them  cause  by  their  constant  attacks  and 
painful  bites  is  sufficient  to  have  made  some  parts  of  the  world 
practically  uninhabitable.  There  are  rich  pieces  of  country  which 
have  remained  absolutely  unsettled  on  account  of  this  pest  alone. 
Some  of  the  choicest  hunting  and  camping  grounds  in  North 
America,  and  in  other  continents  also,  are  practically  closed  to 
the  camper  by  the  countless  millions  of  mosquitoes  which  trans- 
form a  camper's  Paradise  into  an  intolerable  hell,  and  drive  any 
bold  human  invader  to  frenzy.  When  travel  through  such  places 
is  necessary  no  comfort  can  be  hoped  for  without  the  presence 
of  a  dense  smudge  or  without  almost  constant  application  of 
"  mosquito  dope,"  and  even  then  the  unceasing  ''  zangs  "  of  the 
mosquitoes  as  they  threateningly  approach  is  hardly  less  trying 
on  the  nerves  than  are  the  actual  attacks.  Unlike  most  insect 
pests  the  mosquitoes  of  cold  northern  countries  are  if  anything 
more  abundant  than  they  are  in  the  tropics.  The  far  northern 
mosquitoes  do  not,  however,  act  as  carriers  of  disease;  terrible  as 
they  are,  they  wage  clean  warfare,  whereas  tropical  mosquitoes 
have  their  spears  poisoned  with  death-dealing  disease  germs. 
The  northern  mosquitoes  bite,  suck  their  fill  of  blood  if  they  can, 
and  are  through;  the  tropical  mosquitoes  often  leave  months  or 
years  of  suffering  and  disease,  or  even  death,  in  their  wake.  No 
less  than  four  different  diseases  are  believed  to  be  transmitted 
by  mosquitoes  exclusively,  namely,  malaria,  yellow  fever,  dengue 
or  breakbone  fever  and  filariasis,  while  a  fifth,  a  form  of  myiasis 
in  South  America,  is  believed  to  be  transmitted  sometimes  by 
mosquitoes.  Mosquitoes  have  been  suspected  of  complicity  in 
the  transmission  of  still  other  diseases,  but  their  relation  to  the 
first  four  diseases  mentioned  above  is  sufficient  to  brand  them  as 
the  greatest  insect  enemies  of  the  human  race. 

424 


STRUCTURE 


425 


General  Structure.  —  Mosquitoes  are  members  of  the  great 
insect  order  Diptera,  to  which  so  many  human  pests  belong. 
Their  nearest  relatives,  outside  the  mosquito  family  itself,  are 
the  midges  (Chironomidse),  craneflies  (Tipuhdse),  sandflies 
(Phlebotomus),  and  blackflies  or  buffalo  gnats  (Simuliidae) .  The 
members  of  the  mosquito  family,  Culicidae,  can  be  distinguished 
from  other  Diptera  which  look  more  or  less  like  them  by  the 
characteristic  and  quite  conspicuous  fringe  of  scales  on  the  hind 


df.re&.- 


FiG.  188.     Diagram  of  adult  female  mos- 
quito  (Aedes   sollicitans);    abd.,    abdomen; 


Fig.  189.  Digestive  tract  of  a 
mosquito;  d.  f.  res.,  dorsal  food 
reservoirs;  malp.  t.,  malpighian 
tubules;  ph.,  pharynx;  prov.,  pro- 
ventriculus;  rect.,  rectum;  sal.  d., 
salivary    duct;     sal.     gl.,     salivary 


ant.,  antenna;  e.,  eye;  halt.,  haltere;  palp.,     gland;   st.,  stomach;   v.  f.  res.,  ven- 


palpus;   prob.,  proboscis;  th.,  thorax. 


tral  food  reservoir. 


margin  of  the  wings.  Most  of  the  CuUcidae  have  a  long  promi- 
nent proboscis  containing  needle-like  organs  for  piercing  and 
sucking,  but  in  two  subfamilies,  including  the  midges  of  the 
genus  Dixa,  and  the  so-called  phantom  midges,  Corethra  (Fig. 
192),  the  adults  of  which  resemble  true  mosquitoes  and  are  often 
mistaken  for  them,  there  is  no  long  proboscis. 

The  general  appearance  of  adult  mosquitoes  is  so  well  known 


426 


MOSQUITOES 


as  to  need  no  description,  but  the  details  of  their  structure  is  as 
little  known  by  most  people  as  are  those  of  the  structure  of  other 
insects.  The  diagram  on  page  425  (Fig.  188)  illustrates  the 
details  of  the  parts  of  a  mosquito  which  are  of  most  use  in  iden« 
tifying  and  classifying.  The  sexes  can  be  distinguished  most 
readily  by  the  antennae;  in  the  female  (Fig.  190 A)  they  are  long 
and  slender  with  a  whorl  of  short  hairs  at  each  joint,  whereas  in 
the  male  (Fig.  190B)  they  are  shortened  and  have  a  feathery 
appearance,  due  to  tufts  of  long  and  numerous  hairs  at  the 
joints.     In  many  mosquitoes  the  palpi  also  furnish  a  means  of 


Fig.  190.  Heads  of  female  (9)  and  male  (q)  mosquito,  Culiseta  incidens: 
ant.,  antenna;  b.  j.  ant,,  basal  joint  of  antenna;  label,,  labellum;  palp.,  palpus; 
prob.,  proboscis. 


distinguishing  the  sexes;  they  are  usually  long  in  the  males 
but  short  in  the  females,  but  in  Anopheles  they  are  long  in  both 
sexes,  and  in  some  mosquitoes,  e.g.,  Uranotcenia,  they  are  short  in 
both. 

The  proboscis,  which  is  the  most  fearful  part  of  a  mosquito, 
also  differs  in  the  sexes,  and  fortunately  is  so  constructed  in  the 
male  that  a  mosquito  of  this  sex  could  not  pierce  flesh  if  he  would. 
At  first  glance  the  proboscis  appears  to  be  a  simple  bristle,  some- 
times curved,  but  when  dissected  and  examined  with  a  micro- 
scope it  is  found  to  consist  of  a  number  of  needle-like  organs 


STRUCTURE 


427 


lying  in  a  groove  in  the  fleshy  lower  lip,  which  was  the  only  part 
visible  before  dissection.  In  the  female  mosquito  there  are  six 
of  these  needle-hke  organs  the  nature  and  names  of  which  are 
shown  in  Fig.  191.  The  "  labrum-epipharynx "  and  "  hypo- 
pharynx  "  act  together  to  form  a  tube  for  drawing  up  blood  into 
the  mouth.  A  tiny  tube  runs  down  through  the  hypopharynx, 
opening  at  its  tip,  through  which  saliva  is  poured  into  the  wound 
as  through  a  hypodermic  needle  to  prevent  blood  from  coagu- 
lating. The  ensheathing  lower  lip  does  not  itself  penetrate  the 
wound,  but  bows  back  as  the  mosquito  bites,  the  flexible  tip  or 


teph.a» 


palp/ 


Fig.  191.  Side  view  of  head  of  female  Anopheles  showing  mouthparts;  ant., 
antennae;  clyp.,  clypeus;  ceph.  s.,  cephalic  scales;  hyp.,  hypopharynx;  lab., 
labium;  label.,  labellum;  labr.  ep.,  labrum-epipharynx;  mand.;  mandibles;  max., 
maxillae;   palp.,  maxillary  palpi.      X  20.     (After  Nuttall  and  Shipley.) 


*'  labella  "  acting  as  a  guide  for  the  piercing  organs  as  they  are 
sunk  into  the  flesh.  In  male  mosquitoes  the  piercing  organs  are 
much  degenerated,  only  the  suctorial  part  of  the  apparatus  being 
well  developed. 

Besides  the  variations  of  the  parts  mentioned  already,  mos- 
quitoes vary  as  regards  the  form,  distribution,  color  and  other 
characteristics  of  the  scales  which  clothe  much  of  the  body  and  the 
edges  and  veins  of  the  wings;  the  details  of  the  male  reproductive 
organs  at  the  tip  of  the  abdomen;  the  relative  length  of  parts  of 
the  leg;  and  in  other  respects. 

All  mosquitoes  have  good  '*  capacity  "  as  far  as  the  digestive 
tract  is  concerned,  having  three  food  reservoirs  connected  with  the 


428 


MOSQUITOES 


oesophagus,  in  addition  to  a  large  stomach  (Fig.  189).  Connected 
with  the  proboscis  is  a  pair  of  sahvary  glands  consisting  of  three 
lobes  each.  One  of  these  lobes  in  each  gland  differs  from  the 
others  and  instead  of  secreting  ordinary  saliva  is  thought  to  secrete 
the  poisonous  substance  which  prevents  coagulation  of  blood  and 
produces  the  inflammation  and  pain  attendant  upon  a  mosquito 


Fig.  192.  Larva  and  adult  of  Corethra,  a  member  of  the  Culicidae  which  is  not 
a  bloodsucker,  but  is  often  mistaken  for  a  mosquito.  The  larvae  prey  on  mosquito 
larvae  and  other  aquatic  organisms.  Note  anterior  and  posterior  "floats"  in  the 
larva,  and  mosquito-like  appearance  of  adult,  except  for  lack  of  proboscis.  (Larva 
after  Howard,  Dyar  and  Knab;   adult  after  Smith.) 


bite.  Schaudinn,  however,  has  adduced  some  experimental  evi- 
dence that  it  is  the  contents  of  food  reservoirs  which  cause  the 
inflammation.  It  is  in  the  salivary  glands  that  the  malaria  para- 
sites, and  probably  the  parasites  of  dengue  and  yellow  fever  also, 
collect,  and  whence  they  are  poured  with  the  secretions  of  the 
glands  into  the  wounds. 

Life  History.  —  Mosquitoes,  like  other  Diptera,  pass  through 
a  complete  metamorphosis  in  the  course  of  their  life  history,  i.e., 
they  undergo  a  transformation  from  larval  to  adult  stages  during 
a  period  of  rest.  In  a  general  way  the  life  histories  of  all  mos- 
quitoes are  much  alike,  but  in  details  there  is  much  variation 


EGGS 


429 


among  them.  Without  special  adaptations  in  habits  and  physi- 
ology to  meet  the  exigencies  of  their  diverse  environment  there 
would  be  little  chance  for  the  mosquitoes  of  the  frozen  north 
or  of  the  parched  tropical  deserts  to  meet  successfully  the  struggle 
for  existence.  A  great  store  of  interesting  facts  concerning  the 
life  history  and  habits  of  mosquitoes  has  been  collected  by 
Howard,  Dyar  and  Knab  in  Part  I  of  their  ''  Monograph  of  the 


Fig.  193.  Eggs  of  mosquitoes;  A,  Culiseta  inornatus;  B,  Mansonia  perturbans, 
C,  Aedes  calopus;  D,  Anopheles  punctipennis,  dorsal  view;  D',  same,  ventral  view. 
X  75.     (After  Howard,  Dyar  and  Knab.) 

Mosquitoes  of  North  and  Central  America  and  the  West  Indies  " 
and  much  of  the  information  incorporated  into  this  chapter 
has  been  taken  from  their  work. 

The  eggs  of  mosquitoes  (Fig.  193)  are  usually  oval,  with  vari- 
ous surface  markings,  and  in  Anopheles  with  a  peculiar  ''  float  " 
of  air  cells.  The  number  of  eggs  laid  by  a  single  female  mos- 
quito varies  from  40  or  50  to  several  hundred.     Some  species 


430 


MOSQUITOES 


lay  their  eggs  singly  (Fig.  194)  while  others  lay  them  all  at  one 
time  in  little  boat-shaped  rafts  called  egg-boats,  the  individual 
eggs  standing  upright  (Fig.  195).  The  fact  that  the  eggs  are  a 
little  larger  at  the  lower  end  makes  the  whole  egg-boat  slightly 
concave,  thus  making  it  difficult  to  overturn.  Most  of  the  com- 
mon mosquitoes  of  temperate  climates  lay  their  eggs  on  the 

open  surface  of  water  or  at- 
tach them  to  some  partially 
submerged  object;  a  few 
species  lay  eggs  which  sink. 
Many  species,  however, 
especially  those  of  the  far 
north  and  of  the  tropics,  lay 
their  eggs  in  dry  places  which 
are  likely  subsequently  to 
be  covered  with  water.  In 
^     ,„,     ^       ,  ,      ^  ,         J  .  most  mosquitoes  of  temper- 

FiG.  194.     Eggs  of  Anopheles  quadrxmacu-  ^  i  i 

latus    on    surface  of   water.     X    13.     (After    ate    climates   the   eggS   hatch 

Howard.)  jj^  ^  fg^  days,  or  even  within 

24  hours.  In  the  species  of  the  far  north  the  eggs  probably 
never  hatch  until  the  following  spring,  being  laid  in  depressions 
on  the  ground  which  are  usually  not  immersed  until  the  melting 
of  the  winter  snows.  Such  hibernating  eggs  are  said  not  to  hatch 
unless  they  have  been  exposed  to  freezing  temperatures.  On  the 
other  hand  the  mosquitoes 
of  dry  hot  countries  lay 
eggs  which  are  highly  re- 
sistent  to  desiccation  and 
do  not  lose  their  vitality 
during  months  of  dryness. 
Such  species  must  almost 
''live  while  the  rain  falls," 

and  to  win  in  the  struggle  against  an  unfavorable  climate  they 
must  be  prepared  to  utilize  the  most  transitory  pools  for  the 
completion  of  their  aquatic  immature  stages.  In  such  cases 
the  embryo  within  the  egg  shell  develops  to  the  hatching  point, 
so  that  it  is  ready  to  begin  the  larval  existence  almost  with  the 
first  drop  of  rain.  Such  mosquitoes  further  fortify  their  race 
against  the  unkind  environment  by  laying  their  eggs  in  a  number 
of  small  batches  instead  of  in  a  single  mass,  as  is  the  habit  with 


Fig.   195.     Egg  boat  of  Culex  floating  on 
water.      X  about  8. 


LARV/E  OR  "WRIGGLERS"  431 

mosquitoes  where  water  is  plentiful.  Just  as  a  man  runs  less 
risk  of  ruin  if  he  deposits  his  money  in  a  number  of  insecure 
banks  rather  than  in  a  single  uncertain  one,  so  it  is  with  mos- 
quitoes and  the  places  where  they  deposit  their  eggs.  The 
gamble  for  life  in  a  dry  climate  would  be  too  risky  if  all  eggs  were 
deposited  in  one  place,  and  species  with  this  habit  have  probably 
long  since  been  weeded  out  in  the  struggle  for  existence.  An- 
other remarkable  adaptation  of  dry-climate  mosquitoes  is  the 
variation  in  the  hatching  periods  of  the  eggs  in  the  same  batch; 
not  all  hatch  with  the  first  drops  of  moisture,  but  some  lie 
over  until  subsequent  immersions,  thus  insuring  a  much  better 
chance  that  some  of  them,  at  least,  will  not  waste  their  life  on 
the  desert  air  with  too  little  water  to  enable  them  to  reach 
maturity. 

The  eggs  of  mosquitoes  never  hatch  except  in  the  presence  of 
water.  The  larvae,  which  are  always  aquatic,  are  very  active 
wormlike  creatures,  well  known  as  "  wrigglers  "  or  "  wriggle- tails" 
(Fig.  196).  When  first  hatched  they  are  almost  microscopic, 
but  they  grow  rapidly  to  a  length  of  from  a  quarter  of  an  inch  to 
almost  an  inch.  The  bunches  of  long  bristly  hairs  on  the  body 
take  the  place  of  legs,  and  aid  the  larva  in  maintaining  a  position 
in  the  water.  The  ''  rotary  mouth  brush  "  is  a  brush  of  stiff 
hairs  which  is  used  to  sweep  small  objects  toward  the  mouth; 
in  predaceous  species  these  are  sometimes  modified  into  rakelike 
structures  or  into  strong  hooked  bristles  for  holding  prey.  The 
trumpet-shaped  breathing  tube  (Fig.  196 A)  is  present  on  all 
mosquito  larvae  except  Anopheles  (Fig.  196B),  in  which  it  is 
undeveloped.  It  is  used  to  pierce  the  surface  film  of  the  water  to 
draw  air  into  the  air  tubes  or  tracheae  inside  the  body,  for,  al- 
though aquatic,  mosquito  larvae  are  air  breathers,  and  make 
frequent  trips  to  the  surface  to  replenish  their  air  supply,  re- 
maining suspended  by  the  breathing  tube  from  the  surface  of  the 
water  while  breathing.  The  leaf  like  "  tracheal  gills  "  on  the  last 
segment  of  the  abdomen  differ  from  true  gills  in  that  air  tubes 
or  tracheae  instead  of  bloodvessels  ramify  in  them.  In  one 
species  of  mosquito,  Mansonia,  the  larvae  absorb  air  from  the  air- 
carrying  tissues  in  the  roots  of  certain  aquatic  plants,  piercing 
them  with  the  apex  of  the  breathing  tube  and  thus  avoiding  the 
necessity  of  rising  to  the  surface  of  the  water.  In  well-aerated 
water  the  larvae  can  live  without  surface  air  for  a  long  time  by 


432 


MOSQUITOES 


using  their  tracheal  gills,  but  they  die  within  a  few  hours  if 
shut  in  water  without  dissolved  air. 

Mosquito  larvae,  unless  suspended  from  the  surface  film  by 
means  of  the  breathing  tube,  have  a  tendency  to  sink  and  they 
rise  again  only  by  an  active  jerking  of  the  abdomen,  using  it  as 


Fig.  196.  A,  Larva  of  tropical  house  mosquito,  Culex  quinquefasciatus;  ant., 
antennae;  br.  t.,  breathing  tube  or  siphon;  m.  br.,  mouth  brushes;  th.,  thorax; 
8th  s.,  8th  abdominal  segment;  9th  s.,  9th  abdominal  segment;  tr.,  tracheae; 
tr.  g.,  tracheal  gills.  B,  Larva  of  Anopheles  punctipennis;  note  absence  of  breath- 
ing tube,  and  starlike  groups  of  scales  on  abdominal  segments;  m.  br.,  mouth 
brushes;  br.  p.,  breathing  pore;  other  abbrev.  as  on  Fig.  A.  X  10.  (After 
Howard,  Dyar  and  Knab.) 

a  sculling  organ.  Some  species  are  habitual  bottom  feeders, 
others  feed  at  the  surface;  some  live  on  microscopic  organisms, 
others  on  dead  organic  matter,  and  still  others  attack  and  devour 
other  aquatic  animals,  including  young  mosquito  larvae  of  their 
own  and  other  species. 

The  larvae  shed  their  skins  four  times  and  then  go  into  the 


HABITS  OF  ADULTS  433 

resting  pupal  stage.  Mosquitoes  of  temperate  climates  usually 
take  from  five  days  to  two  weeks  to  complete  the  larval  existence, 
depending  almost  entirely  on  temperature.  In  the  mosquitoes 
adapted  to  take  advantage  of  transitory  rain-pools  the  larvje  may 
transform  into  pupse  within  two  days  and  the  pupal  stage  is  a 
mere  matter  of  hours.  On  the  other  hand,  some  mosquitoes 
habitually  pass  the  winter  as  larvae. 

The  general  form  of  the  pupa  can  be  seen  in  Fig.  197.  Alcock 
has  aptly  described  this  stage  of  a  mosquito  as  resembling  a 
tiny  lobster  deprived  of  ap-  . 

pendages  and  carrying  its 
tail  bent.  The  pair  of  ear- 
like breathing  tubes  on  the 
cephalothorax  (head  and 
thorax  fused)  take  the  place 
of  the  trumpet-like  tube  of  eye  -• 
the  larva  and  are  used  in 
the  same  manner.  Unlike 
the  larva  the  pupa  is  lighter  win9.c.' 

than    water,   and    requires 

muscular  effort  to  sink  in-        ^ig.   197.     Pupa  of  house  mosquito,  Culex 

pipiens:   ant.  c,  antennal  case;   br.  t.,  breath- 
Stead  01  to  rise.  Ing  tubes;    leg.  c,   leg  cases;    pad.,   paddles; 

As  remarked  before,  the  ^^^s  «-  ^^^s  ^^s^-    x  ^o.    (After  Howard, 

Dyar  and  Knab.) 

transiormation     into     the 

adult  during  the  pupal  stage  may  be  a  matter  of  a  few  hours  in 
the  case  of  the  dry-climate  mosquitoes,  but  in  most  species  it  re- 
quires from  two  days  to  a  week,  depending  on  the  temperature. 
The  adult  mosquito  emerges  head  first  through  a  longitudinal 
slit  along  the  back  of  the  thorax.  After  its  exit  it  rests  for  a 
moment  on  the  old  pupa  skin,  stretches  and  dries  its  wings,  and 
then  takes  flight. 

Habits  of  Adults.  —  Adult  mosquitoes  vary  to  a  remarkable 
degree  as  regards  habitats,  feeding  habits,  mode  of  hibernation, 
choice  of  breeding  grounds,  and  other  habits.  The  knowledge, 
only  recently  gained,  that  each  species  of  mosquito  has  habits 
and  habitats  more  or  less  peculiar  to  itself,  is  of  great  economic 
importance,  since  it  does  away  with  useless  expenditure  in  com- 
bating harmless  or  relatively  harmless  species,  and  aids  in  the 
fight  against  particularly  noxious  ones.  The  fact,  for  instance, 
that  one  of  the  commonest  summer  mosquitoes  of  northeastern 


434  MOSQUITOES 

United  States,  Culex  territans,  does  not  annoy  man  does  away 
with  the  necessity  of  combating  this  species,  and  obviates  the 
necessity  of  destroying  larvae  in  certain  kinds  of  marshes  and 
pools  where  this  is  practically  the  only  breeder.  Again,  the 
fact  that  mosquitoes  breeding  in  crab  holes  do  not  annoy  man 
eliminates  the  necessity  of  attempting  the  almost  impossible 
task  of  destroying  such  breeding  grounds  in  order  to  be  free  of 
mosquitoes.  The  fact  that  a  certain  species  of  Anopheles,  A. 
malefactor,  which  is  a  tree-hole  breeder,  is  not  a  malaria  carrier, 
saved  thousands  of  dollars  in  the  anti-malarial  fight  in  the 
Canal  Zone. 

Habitats.  —  A  classification  of  mosquitoes  according  to  habi- 
tats and  breeding  grounds  has  been  attempted  by  some  authors. 
Dr.  J.  B.  Smith,  for  instance,  divides  the  mosquitoes  of  New 
Jersey  into  four  ecologic  groups,  the  salt  marsh,  house,  swamp, 
and  woodland  mosquitoes.  However,  almost  as  many  different 
ecologic  groups  could  be  made  as  there  are  species  of  mosquitoes 
or  possible  breeding  and  foraging  places.  There  are  species 
which  breed  in  reedy  swamps,  woodland  pools,  eddies  of  rivers, 
slow-flowing  streams,  holes  in  trees,  pools  of  melted  snow,  salt 
marshes,  tide  pools,  crab  holes,  pitcher  plants  and  other  water- 
bearing plants,  or  in  broken  bamboo  stems  filled  with  water. 
There  are  species  which  have  become  "  domesticated  "  and  occur 
almost  always  in  the  vicinity  of  houses,  laying  their  eggs  in 
water  troughs,  street  gutters,  rain  barrels,  water-filled  cans  in 
garbage  heaps,  flower  vases,  water  bottles,  and  any  other  col- 
lection of  water  in  or  about  human  habitations.  Some  species 
show  almost  no  preference  as  regards  breeding  places,  others, 
especially  those  breeding  in  such  specialized  places  as  in  water- 
holding  plants,  are  very  closely  limited ;  some  species  prefer  pure 
clear  water,  others  filthy  water,  while  still  others  are  apparently 
indifferent. 

Migration.  —  That  mosquitoes  are  seldom  found  far  from 
their  breeding  grounds  is  another  fact,  only  recently  recognized, 
of  great  economic  importance.  The  evidence  points  to  the  fact 
that  most  kinds  of  mosquitoes  seldom  stray  more  than  from  half 
to  three-quarters  of  a  mile  from  their  birthplace,  and  usually  not 
over  a  few  hundred  yards.  The  supposition  that  mosquitoes 
utilize  a  strong  wind  to  carry  them  long  distances  is  entirely  false, 
since  mosquitoes  are  so  delicate  as  to  be  unable  to  fly  at  all  with  a 


TIME  OF  ACTIVITY  435 

strong  wind  but  remain  hidden  away  at  times  when  such  wind 
storms  occur.  Some  mosquitoes  are  able  to  resist  moderate  winds, 
but  nearly  always  fly  against  them  instead  of  with  them.  The  salt 
marsh  mosquitoes  are  apparently  an  exception  to  the  sedentary 
nature  of  mosquitoes,  as  shown  by  Smith's  work  in  New  Jersey. 
These  mosquitoes  commonly  migrate  for  a  number  of  miles  and 
may  go  as  much  as  40  miles  inland  from  the  salt  marshes  which 
bred  them.  The  common  salt  marsh  mosquito,  Aedes  sollicitans 
(Fig.  188),  the  mosquito  that  made  New  Jersey  famous,  breeds  in 
enormous  numbers  in  the  extensive  coastal  marshes  of  New 
Jersey,  whence  it  migrates  inland,  and  sometimes  crosses  the 
Hudson  River  and  invades  New  York  City  in  hordes.  The 
author  has  seen  mosquitoes  (not  positively  identified  as  this 
species)  literally  in  clouds  on  the  roofs  of  buildings  in  the  down- 
town section  of  New  York,  where  the  day  before  not  a  mosquito 
was  to  be  found.  With  the  exception  of  a  few  of  the  salt  marsh 
species,  however,  an  abundance  of  mosquitoes  can  almost  al- 
ways be  looked  upon  as  evidence  of  the  existence  of  breeding 
places  within  a  mile,  and  usually  within  a  few  hundred  yards. 

Although  most  species  are  not  migratory,  railroad  trains, 
street  cars,  ships  and  other  conveyances  are  efficient  means  of 
transfer  for  mosquitoes.  Hawaii  is  said  to  have  been  free  of 
these  pests  until  they  were  introduced  with  sailing  vessels,  in 
which  mosquitoes  can  usually  find  plenty  of  water  for  breeding. 
The  great  number  of  trains  daily  running  inland  in  New  Jersey 
from  the  marsh-studded  coast  is  undoubtedly  a  factor  in  keeping 
more  distant  suburban  towns  stocked.  Well  established  cases 
are  on  record  of  places  once  free  of  mosquitoes  becoming  infested 
after  the  advent  of  railroad  train  or  boat  service. 

Time  of  Activity.  —  Although  mosquitoes  are  usually  looked 
upon  as  strictly  nocturnal,  and  though  this  is  true  of  most  of 
the  common  species  of  temperate  climates,  it  is  by  no  means 
characteristic  of  the  whole  group.  Many  species,  including  all 
Anopheles,  are  active  chiefly  at  twilight,  in  the  evening,  or  early 
morning.  Knab  found  that  the  mosquitoes  of  northern  prairies, 
where  the  nights  are  too  cold  for  them,  are  active  throughout  the 
day  only.  A  large  proportion  of  forest-Hving  tropical  species, 
at  least  in  America,  are  said  to  be  diurnal.  Some  of  the  mos- 
quitoes of  the  northern  woods  are  apparently  ready  to  bite 
when  a  victim  approaches,  whether  it  be  day  or  night.     The 


436  MOSQUITOES 

widely  distributed  yellow  fever  mosquito,  Aedes  calopus  (or 
Stegomyia  fasciata)  (Fig.  201),  feeds  by  preference  in  the  early 
morning  or  late  afternoon.  Here  again  a  knowledge  of  the 
habits  of  particular  species  is  of  importance,  since  it  may  aid  in 
the  intelligent  avoidance  of  particular  disease-carrying  forms. 

Food  Habits.  —  Heretical  as  it  may  sound,  mosquitoes  feed 
mainly  on  plant  juices,  honey,  etc.  It  is  doubtful  if  the  males 
of  any  species  normally  suck  blood,  and  even  the  females  of  some 
species  are  strict  vegetarians.  On  the  other  hand,  the  females 
of  many  species  have  a  voracious  craving  for  warm  blood.  Some 
species  indiscriminately  attack  any  warm-blooded  or  even  cold- 
blooded animal,  while  others  show  strong  preferences.  The 
yellow  fever  mosquito  normally  feeds  chiefly  on  man,  and  even 
discriminates  against  the  black  race.  The  other  "  domestic  " 
mosquitoes  apparently  have  a  strong  liking  for  human  blood  also, 
and  it  is  not  unlikely  that  their  domestic  habits  are  the  result 
of  their  taste  for  human  blood.  Knab  found  that  Aedes  spenceri 
of  the  Saskatchewan  prairies  would  fly  toward  any  large  object. 
On  the  prairies  such  an  object  would  usually  be  a  large  animal 
and  the  mosquitoes  would  fly  toward  it  instinctively  in  the 
hope  of  satiating  the  craving  for  food. 

Hibernation.  —  The  method  employed  by  mosquitoes  for 
passing  the  winter  in  cold  climates,  and  the  dry  season  in  the 
tropics,  varies  with  the  species.  Many  of  the  mosquitoes  of 
temperate  climates  and  many  in  the  tropics  hibernate  or  pass  the 
dry  season  in  the  adult  stage,  the  females  stowing  themselves 
away  in  hollows  in  trees,  caves,  crevices  in  rocks,  cellars,  barns, 
etc.,  to  come  forth  and  lay  their  eggs  in  the  spring.  A  few  species 
hibernate  in  the  larval  stage,  the  larvae  of  one  species,  Wyeo- 
myia  smithii,  becoming  enclosed  in  solid  ice  in  the  leaves  of  the 
pitcher  plant  in  which  they  live.  Most  hibernating  larvae  retire 
to  the  bottom  of  their  breeding  pools  during  cold  weather  and 
do  not  survive  freezing.  The  majority  of  temperate-  and  warm- 
climate  mosquitoes  and  all  of  the  northern  ones  pass  the  un- 
favorable season  in  the  egg  state,  and  this  may  be  looked  upon  as 
the  common  method  of  hibernation. 

Length  of  Life.  —  The  length  of  life  of  mosquitoes  varies  with 
the  species  and  with  the  sex.  Male  mosquitoes  seldom  live  more 
than  from  one  to  three  weeks;  their  duty  in  life  is  done  when  they 
have  fertilized  the  females.     The  latter  usually  die  shortly  after 


I 


CLASSIFICATION  437 

they  have  laid  their  eggs  but  some  species  may  live  for  four  months 
or  more.  The  species  which  lay  all  their  eggs  in  a  mass  at  one 
time  are  short  lived,  and  have  several  generations  a  year,  whereas 
those  in  which  the  eggs  are  laid  in  small  lots,  at  intervals,  live  for 
several  months.  Species  in  which  the  females  hibernate  are  still 
longer  lived,  but  since  they  are  not  active  in  winter  their  effec- 
tive life  is  short. 

Classification.  —  Over  500  species  of  mosquitoes  have  been 
described,  the  majority  of  which  belong  in  the  tropics,  although 
the  north  is  richer  in  individuals.  The  task  of  classifying  all  of 
these  species  into  subfamilies  and  genera  is  one  which  has  taxed 
the  wits  of  many  scientists.  The  wide  discrepancies  in  the  work 
of  different  men  as  regards  mosquito  classification  is  the  best 
possible  proof  of  the  difficulties  in  the  way.  As  in  many  other 
groups  of  animals,  intensive  study  has  tended  to  magnify  the 
value  of  certain  characteristics  as  criteria  of  genera  or  subfamilies, 
the  result  being  the  breaking  up  of  what  would  ordinarily  be 
looked  upon  as  a  single  group  into  a  number  of  poorly  defined 
and  intergrading  groups.  Theobald,  who  has  written  a  mono- 
graph of  the  mosquitoes  of  the  world,  separates  the  Corethrinae 
(forms  without  a  long  proboscis)  from  the  mosquitoes,  and 
divides  the  remainder  of  the  family  into  ten  subfamilies  and  a 
very  large  number  of  genera  based  largely  on  scale  character- 
istics. On  the  other  hand,  Howard,  Dyar  and  Knab,  whose  classi- 
fication is  adopted  here,  recognize  only  two  subfamilies  —  the  Core- 
thrinae and  the  Culicinae,  the  latter  including  all  the  true  mos- 
quitoes. The  Culicinae  are  further  divided  into  two  tribes,  the 
Sabethini,  including  chiefly  forest-dwelling  non-blood-sucking 
forms,  and  the  Culicini.  The  genera  of  the  latter  are  arranged 
in  a  series  from  the  primitive  forms  of  the  genus  Anopheles  to 
such  highly  specialized  forms  as  Megarhinus. 

The  identification  of  species  of  mosquitoes,  or  even  of  genera, 
is  often  very  difficult  for  anyone  but  a  specialist.  Fortunately 
some  of  the  most  important  disease-carrying  species  are  so 
marked  that  they  can  quite  readily  be  distinguished  even  by 
a  novice.  Only  a  few  of  the  disease-bearing  species  can  be 
separately  described  here. 


438 


MOSQUITOES 


Mosquitoes  and  Malaria 

As  was  shown  in  Chap.  IX,  malaria  is  one  of  the  most  important 
and  one  of  the  most  deadly  of  human  diseases.  This  being  true, 
the  mosquitoes,  which  are  the  sole  means  of  transmitting  the 
disease,  must  be  looked  upon  as  among  the  most  important  and 
most  deadly  enemies  of  the  human  race.  The  role  of  mosquitoes 
in  causing  disease,  especially  malaria,  has  been  suspected  by 
various  peoples  as  far  back  as  any  records  go.  The  steps  which 
led  to  the  proof  of  the  relation  of  mosquitoes  to  malaria  are  briefly 
outlined  on  pp.  148-149. 

Fortunately  not  all  mosquitoes  are  malaria  carriers;  in  fact, 

only  one  genus,  Anopheles,  com- 
prising a  number  of  more  or  less 
well-defined  subgenera  which  have 
been  considered  genera  by  some 
workers,  is  known  to  be  able  to 
transmit  the  human  malarial  dis- 
eases, and  not  even  all  of  the 
species  of  this  genus  are  incrimi- 
nated. As  will  be  seen  below, 
some  species  of  Anopheles  are  able 
to  transmit  one  type  of  malaria, 
but  not  another.  A  species  of 
Culex  has  been  shown  to  be  instru- 
mental in  transmitting  a  disease 
of  birds  which  is  allied  to  malaria. 
The  role  of  the  mosquito  in  the 
A.aibimanus.  Drawn  to  scale.  (After  spread  of  malaria  and  the  develop- 

Howard,  Dyar  and  Knab.)  ^  .  .        , 

ment  of  the  parasites  in  the  mos- 
quito's body  have  been  discussed  in  Chap.  IX,  pp.  154-156.  Suffice 
it  to  repeat  here  that  the  sexual  phase  of  the  life  history  of  all 
malaria  parasites  occurs  in  the  digestive  tract  of  mosquitoes,  after 
which  a  rapid  multiplication  of  the  germs  takes  place,  resulting 
ultimately  in  the  collection  of  large  numbers  of  the  parasites  in 
the  salivary  glands  of  the  insect,  whence  they  are  poured  into  the 
capillaries  in  the  skin  of  the  subsequent  victims  of  the  mosquito. 
Identification  of  Anopheles.  —  The  Anopheles  mosquitoes, 
fortunately,  are  fairly  easy  to  identify  in  all  stages  of  their  de- 
velopment except  as  pupae.     They  represent  a  primitive  group 


Fig.  198.  Wings  of  American 
Anopheles;  A,  A.  crucians;  B,  A.  quad- 
rimaculatus;    C,  A.  punctipennis;    D, 


f 


MALARIA-CARRYING  SPECIES  OF  ANOPHELES         439 

of  mosquitoes,  and  in  many  respects  are  less  specialized  than 
other  members  of  the  family.  The  different  species  of  the 
genus  vary  a  great  deal  as  regards  choice  of  breeding  places, 
habits  and  appearance,  so  that  it  is  necessary  in  any  malarial 
district  to  determine,  if  possible,  which  species  are  malaria 
carriers,  how  they  may  be  identified,  where  they  breed,  and  what 
their  habits  are.  The  majority  of  the  species  have  mottled  or 
spotted  wings,  and  the  arrangement  of  the  markings  is  a  good 
means  of  identification  (Fig.  198). 

The  following  comparative  table  (Fig.  199)  shows  in  a  graphic 
way  how  Anopheles  may  ordinarily  be  distinguished  from  other 
common  mosquitoes,  such  as  Culex,  Aedes,  etc.,  in  their  different 
stages. 

Malaria-Carrying  Species.  —  Over  a  hundred  species  of  Anoph- 
eles have  been  described  and  they  occur  all  over  the  temperate 
and  tropical  parts  of  the  world.  Although  not  more  than  about 
half  of  these  species  have  been  proved  to  be  able  to  harbor  ma- 
larial parasites  and  nurse  them  to  the  weaning  point,  the  num- 
ber of  incriminated  species  is  constantly  growing,  and  it  is  the 
safest  plan  to  look  upon  any  Anopheles  as  a  potential  malaria 
carrier  until  proved  otherwise.  The  fact  that  a  given  species 
of  Anopheles  may  transmit  one  type  of  malaria  but  not  another 
complicates  the  task  of  determining  the  role  of  a  species,  and  has 
caused  discrepancies  in  the  results  of  workers.  A.  quadri- 
maculatus  (Fig.  200)  in  North  America,  for  instance,  may  carry 
tertian  and  quartan  malaria,  but  not  the  more  deadly  aestivo- 
autumnal  type.  A.  crucians,  on  the  other  hand,  carries  sestivo- 
autumnal  malaria  but  only  rarely  carries  tertian  malaria.  The 
third  common  North  American  species,  A.  punctipennis,  has 
recently  been  proved  to  be  able  to  nurse  and  transmit  tertian 
and  quartan  malaria,  but  not  nearly  so  readily  as  does  A.  qua- 
drimaculatus.  The  situation  among  these  American  species 
fairly  illustrates  what  is  found  elsewhere  —  considerable  differ- 
ences among  the  species  of  Anopheles  as  regards  their  ability  to 
nurse  the  several  types  of  malaria  and  the  readiness  with  which 
they  may  do  so.  In  most  countries,  though  there  may  be  several 
species  which  transmit  malaria,  there  is  usually  one  species  which 
is  especially  responsible  for  the  disease.  In  North  America  it  is 
A.  quadrimaculatus  and  in  the  southern  states  A.  crucians  and 
quadrimaculatus ;  in  tropical  parts  of  America,  A.  alMmanus  and 


440 


MOSQUITOES 


Anopheles 


Culex,  Aedes,  etc. 


EGGS 
Eggs  laid  singly  on  surface  of  water;  Eggs  laid  in  rafts  or  egg-boats,   or 

provided  with  a  partial  envelope,  more       singly  on  or  near  water,  or  where  water 
or  less  inflated,  acting  as  a  "float."  may  accumulate;    never  provided  with 

a  "float." 


LARV^ 


LarvfiB  have  no  long  breathing  tube  or 
siphon;  rest  just  under  surface  of  water 
and  lie  parallel  with  it. 


Larvae  have  distinct  breathing  tube 
or  siphon  on  8th  segment  of  abdomen; 
hang  from  surface  film  by  this  siphon, 
except  in  Mansonia,  which  obtains  air 
from  aquatic  plants. 


PUP^ 
Pupae    have   short    breathing   trum-  Pupae  have  breathing  trumpets  of  va- 

pets;  usually  do  not  hang  straight  down       rious  length;  often  hang  nearly  straight 
from  surface  of  water.  down  from  surface  of  water. 


HEADS   OF  ADULTS 
Palpi  of  both  male  and  female  long  Palpi  of  female  always  much  shorter 

and  jointed,  equaling  or  exceeding  the       than  proboscis,  those  of  male  usually 
proboscis  in  both  sexes.  long,  but  sometimes  short. 


RESTING    POSITION   OF   ADULT 


Adult  rests  with  body  more  or  less  at 
angle  with  surface,  the  proboscis  held 
in  straight  line  with  body. 


Adult  usually  rests  with  body  parallel 
to  surface,  though  sometimes  at  an 
angle.  Proboscis  not  held  in  straight 
line  with  body,  giving  "  hump-backed  " 
appearance. 


FiQ.  199. 


HABITS  OF  ANOPHELES  441 

argyrotarsus ;  in  Europe,  A.  maculipennis ;  in  Africa,  A,  costalis  and 
funesta;  in  India,  A.  culidfacies,  stephensi  and  listoni;  in  Malay 
countries,  A.  umbrosus  and  willmori;  in  China  and  Japan,  A,  sinen- 
sis and  listoni;  in  the  East  Indies,  A.  ludlowi;  and  in  Australia, 
A .  hancrofti.  These  species  are  only  a  few  of  the  most  widely  dis- 
tributed and  commonest  of  the 
malaria  carriers.  Many  other  spe- 
cies may  be  locally  more  important. 
Habits  of  Anopheles.  —  Be- 
sides the  ability  to  nurse  the 
parasites  of  malaria,  an  efficient 
malaria  spreader  must  have  habits 
which  will  insure  the  use  of  such 
ability.  The  important  malaria 
carriers  are,  therefore,  species 
which  readily  attack  man,  and 
especially  those  which  are  more 

or  less    ''domesticated."       Nearly        Fig.     200.      The    common    North 
n  .  f>    A  77  , .         American  malarial  mosquito,  Anoph- 

all  species  of  Anopheles  are  active  ^i^,  quadHmaculatus. 
only  at  twilight,  and  forage  out- 
doors neither  in  bright  daylight  nor  in  the  darkness  of  night, 
though  such  species  may  bite  at  any  hour  of  the  day  inside  houses. 
Different  species  are  known  to  come  forth  at  different  times 
in  the  evening,  some  with  the  first  shade  of  the  late  afternoon, 
others  not  until  almost  dark.  A  few  species,  e.g.,  A.  hraziliensis, 
are  diurnal,  and  many  forest  species  will  readily  bite  in  the  day- 
time if  disturbed.  Nearly  all  Anopheles  hibernate  as  adults, 
but  a  few,  notably  A.  bifurcatus  of  Europe,  hibernate  as  larvae. 
Anopheles  may  breed  in  almost  any  standing  water  providing 
it  contains  microscopic  organisms  on  which  to  feed.  Dr.  Smith, 
of  New  Jersey,  says  he  has  found  no  pool  so  insignificant  and 
no  stream  so  rapid  that  Anopheles  could  not  breed  in  it  some- 
where. He  says  ''  no  other  mosquito  has  as  wide  a  range  of 
breeding  places  as  have  the  species  of  Anopheles.'^  Nevertheless, 
it  is  apparently  true  that  each  species  has  its  favorite  breeding 
grounds  and  some  species  are  quite  particular.  A.  willmori 
of  the  hilly  parts  of  Malay,  for  instance,  will  breed  only  in  swift- 
running  streams,  the  banks  of  which  are  cleared,  whereas  A. 
umbrosus  of  the  coastal  plains  of  the  same  country  breeds  only 
in  jungle-edged  streams;    A.  eiseni  of  Central  America   breeds 


442  MOSQUITOES 

only  in  tree  holes;  A.  cruzi  of  Brazil  breeds  in  accumulations  of 
water  in  the  leaves  of  certain  tropical  plants.  A  number  of 
species  of  Anopheles  will  breed  in  brackish  water,  and  some  in 
pure  or  even  concentrated  sea  water.  A.  ludlowi  of  the  Philip- 
pines is  believed  to  breed  only  in  sea  water.  Some  of  the  coral 
islands  of  the  East  Indies  are  practically  uninhabitable  for  new- 
comers on  account  of  the  prevalence  of  malaria  which  is  carried 
by  Anopheles  that  breed  in  quiet  pools  within  the  coral  reefs. 

The  larvae  of  Anopheles  are  chiefly  surface  feeders.  Some  feed 
upon  anything  floating  on  the  surface  of  the  water  which  is 
small  enough  to  enter  the  mouth.  Others,  however,  reject  many 
things  after  they  have  been  swept  into  the  mouth  by  the  mouth 
brushes,  and  some  feed  exclusively  on  vegetable  matter.  Only 
a  few  species  are  predaceous. 

Apparently  neither  the  eggs  nor  larvae  of  Anopheles  are  resistant 
to  drying,  though  they  may  live  on  moist  mud  for  some  time. 
Eggs  of  Anopheles  laid  in  such  mud  develop  to  the  hatching  point 
but  do  not  hatch  until  immersed,  and  die  if  the  mud  dries  to  the 
extent  of  losing  its  glistening  surface. 

Anopheles  are  not  rapid  in  development  as  compared  with 
some  mosquitoes.  At  Washington,  D.  C,  in  early  summer,  A, 
quadrimaculatus  was  determined  by  Dr.  Howard  to  develop  in  a 
minimum  of  24  days  —  three  for  the  eggs,  16  for  the  larvae,  and 
five  for  the  pupae.  In  some  species  the  development  may  be 
more  rapid,  but  about  two  weeks  is  probably  a  minimum.  Ac- 
cording to  observations  by  Kulagin  near  Moscow,  Russia,  in 
1906,  there  was  but  one  generation  of  Anopheles  in  a  year,  the 
females  always  resting  over  winter  before  depositing  their  eggs. 
This  point  of  the  number  of  generations  of  Anopheles  deserves 
further  local  study  everywhere. 

It  is  important  to  note  that  Anopheles  mosquitoes  are  verj'' 
sedentary  in  habit,  and  seldom  fly  more  than  a  few  hundred 
yards  from  their  birthplace,  and  usually  not  this  far.  As  a 
group,  the  insects  of  this  genus  are  physically  incapable  of  as  long 
flight  as  are  most  other  mosquitoes.  It  is  frequently  reported 
that  Anopheles  is  found  several  miles  from  its  nearest  breeding 
places,  but  the  difficulty  of  knowing  with  certainty  that  no 
water-filled  hoofprint  or  tin  can  exists  in  the  intervening  area  is 
obvious.  That  an  Anopheles  may  occasionally  wander  half  a 
mile  or  more  from  its  breeding  ground  is  unquestionable,  but  not 


AEDES  CALOPUS  AND  YELLOW  FEVER       443 

enough  individuals  do  this  to  make  it  necessary  to  look  for 
breeding  places  more  than  three  or  four  hundred  yards  from  the 
infested  locality.  The  conveyance  of  mosquitoes  in  trains, 
boats,  etc.,  must,  however,  be  taken  into  account. 

The  effect  of  smti- Anopheles  campaigns  on  the  prevalence  of 
malaria  is  discussed  in  Chap.  IX,  pp.  165-167. 

Mosquitoes  and  Yellow  Fever 

Following  upon  the  heels  of  the  discovery  of  the  relation  of 
mosquitoes  to  malaria,  and  second  only  to  it  in  importance,  came 
the  discovery  of  a  similar  relation  to  yellow  fever,  in  1900.  As 
in  the  case  of  malaria,  some  physi- 
cians suspected  the  instrumentality 
of  mosquitoes  in  the  dissemination  of 
this  disease  before  there  was  any 
proof  of  it.  The  proof  came  as  the 
result  of  the  illustrious  work  of  the 
American  Army  Yellow  Fever  Com- 
mission, composed  of  Doctors  Reed, 
Carroll,  Lazear,  and  Agramonte,  at 
the  cost,  indirectly,  of  the  lives  of 
three  of  them.  What  is  known  of 
the  nature  of  yellow  fever,  and  of 
the  role  of  the  mosquito  in  trans- 
mitting it,  is  discussed  in  Chap.  X, 
pp.  182-185.  It  should  be  repeated 
here,  however,  that  the  ''germ"  of  the 
disease  is  still  unknown,  though  be- 
lieved to  be  a  protozoan.    The  blood 

of   a   patient   can   infect    a    mosquito        Fig.    201.     Yellow   fever    mos- 
ij.         j.T-£j.j.T_  1  r    quito,      Aedes     calojms,     female. 

only  durmg  the  first  three  days  of   (After  Doane.) 

illness,    and    the    mosquito    cannot 

transmit  the  disease  in  less  than  12  days  later.     In  one  case, 

hereditary  transmission  of  yellow  fever  from  an  infected  mosquito 

to  its  offspring  has  been  shown  to  occur. 

The  Transmitting  Species,  Aedes  calopus.  Unlike  the  condi- 
tion as  regards  malaria,  yellow  fever  can  be  transmitted  by  only 
one  species  of  mosquito,  Aedes  calopus  (or  Stegomyia  fasciatus) 
(Fig.  201).  This  is  a  small  black  mosquito,  conspicuously 
marked  by  white  bands  on  the  legs  and  abdomen,  and  a  white 


444 


MOSQUITOES 


Fig.  202.  Head  of  Aedes 
calopus,  male.  (After  Gold- 
berger.) 


lyre-shaped  design  on  the  thorax.  The  female,  which,  of  course, 
is  the  only  sex  connected  with  the  transmission  of  disease,  since 
the  males  do  not  suck  blood,  has  very  short  palpi  which  are  white 
at  the  tip.     The  wings  are  clear  and  somewhat  iridescent. 

Habits  of  Aedes  calopus.  —  The  yellow  fever  mosquito  is  the 
most  thoroughly  "  domesticated  "  species  known.  It  is  seldom 
found  except  in  the  vicinity  of  houses  and  shows  a  decided  pre- 
ference for  human  blood.  As  a  rule  it 
seldom  leaves  the  rooms  of  houses  ex- 
cept to  find  a  suitable  place  to  lay  its 
eggs.  Long  familiarity  with  man  has 
made  this  mosquito  one  of  the  most 
elusive  and  well-adapted  pests  .of  the 
human  race  which  nature  has  ever 
evolved.  Its  stealthy  attack  from  be- 
hind; its  habit  of  crawling  up  under  the 
clothing  to  bite  in  preference  to  attack- 
ing the  exposed  ankles;  the  suppres- 
sion of  the  characteristic  mosquito 
"song,"  so  that  its  bite  comes  silently 
and  without  warning;  its  habit  of  concealing  itself  in  pockets, 
folds,  etc.,  of  garments;  its  hiding  behind  pictures,  under  chairs, 
etc.;  the  wariness  of  its  larvae;  —  all  these  are  the  result  of 
lessons  learned  from  long  and  close  association  with  man. 

Aedes  calopus  is  principally  a  diurnal  mosquito,  and  becomes 
particularly  hungry  in  the  early  morning  and  during  the  after- 
noon. It  will  bite  in  lighted  rooms,  but  will  never  bite  in  the 
dark.  The  French  Yellow  Fever  Commission  in  Rio  de  Janeiro 
stated  that  Aedes  calopus  is  nocturnal.  The  evidence  for  this 
conclusion,  which  is  at  variance  with  the  observations  of  other 
workers,  has  been  shown  by  Howard,  Dyar  and  Knab  to  be  very 
inadequate  and  faulty.  The  danger  of  sleeping  in  an  infected 
place,  and  the  comparative  freedom  from  danger  enjoyed  by 
persons  who  visit  infected  places  only  in  the  daytime,  is  thought 
to  be  due  to  the  fact  that  most  of  the  mosquitoes  obtain  a  meal 
very  early  in  the  morning,  just  after  daybreak. 

Breeding.  —  A  edes  calopus  never  lays  eggs  until  it  has  had  a 
meal  of  blood  and  when  water  or  moist  surfaces  are  available. 
According  to  recent  experiments  by  Bacot  a  single  male  mosquito 
may  fertilize  a  number  of  females.     Fertile  eggs  are  usually 


BREEDING    OF    AEDES  CALOPUS  445 

laid  from  four  to  seven  days  after  a  blood  meal.  The  nearest 
allies  of  this  species  are  tree-hole  breeders,  but  the  yellow  fever 
mosquito  has  become  domesticated  to  such  an  extent  as  to  much 
prefer  a  rain  barrel  or  water-filled  tin  can  in  a  garbage  heap,  or, 
even  better,  a  water-pitcher  or  flower-vase  indoors.  Churches 
in  Central  America  are  usually  well  supplied  with  yellow  fever 
mosquitoes  which  breed  in  the  holy-water  fonts. 


Fig.  203.     A  yellow  fever  center  in  Panama  in  the  pre- American  days.     (Drawn 
from  photo  from  Thompson.) 

The  eggs  (Fig.  193C),  up  to  150  in  number,  are  laid  in  several  lots 
at  intervals  of  a  few  days,  either  on  the  surface  of  the  water,  or,  as 
is  more  common,  on  the  edges  of  the  container,  or  on  a  partially 
submerged  object,  wherever  a  moist  surface  is  presented  and  where 
a  slight  elevation  of  the  water  will  submerge  them.  The  female 
mosquitoes  die  a  short  time  after  the  last  batch  of  eggs  is  laid. 
According  to  Bacot's  experiments  the  promptness  of  hatching 
depends  on  temperature  and  on  whether  the  eggs  have  been  kept 
under  moist  or  dry  conditions.  The  eggs  of  this  species  retain 
their  vitality  for  several  months  when  kept  absolutely  dry,  but 
they  hatch  more  readily  and  with  less  mortality  if  kept  moist. 
When  the  eggs  are  laid  directly  on  the  surface  of  water  they  ma- 
ture less  rapidly  than  when  laid  above  the  surface,  probably  on 
account  of  the  cooling  effect  of  the  water.  Eggs  laid  on  the 
surface  hatch  in  a  minimum  of  two  days,  while  those  above  it, 
if  later  submerged,  may  hatch  in  less  than  12  hours.  According 
to  recent  work  by  Atkin  and  Bacot,  eggs  will  not  hatch  in  sterile 
water,  but  will  hatch  within  a  few  hours  after  the  introduction  of 
living  bacteria.     The  larvae  (Fig.  204)  thrive  in  either  clean  or  foul 


446 


MOSQUITOES 


water  and  even  in  brackish  water,  provided  food  material,  in  the 
form  of  dead  organic  matter  and  the  accompanying  bacteria,  is 
present.  Atkin  and  Bacot  have  recently  shown  that  the  food 
consists  almost,  if  not  quite,  exclusively  of  bacteria,  and  that 

when  the  larvae  are  present  in  large 
numbers  they  exert  a  considera- 
ble influence  in  the  purification  of 
water.  Often  the  larvae  are  over- 
looked, since  they  immediately 
wriggle  to  the  bottom  of  their 
dwelling  place  when  approached, 
and  hug  the  bottom  so  closely  that 
even  if  a  barrel  containing  thousands 
of  them  is  turned  over  on  its  side, 
about  80  per  cent  will  stay  in  the 
little  remaining  water.  The  larvae 
feed  exclusively  on  the  bottom  and 
can  often  be  seen  nibbling  away 
at  a  dead  insect  or  bit  of  decaying 
vegetation.  With  plenty  of  food 
and  at  favorable  temperatures  the 
larval  existence  may  be  completed 
in  four  days,  according  to  Bacot, 
though  it  usually  requires  a  longer 
time  than  this,  and  may  be  drawn 
out  to  two  months  or  more.  The 
larvae  are  not  resistant  to  dry- 
ing, and  die  in  a  few  hours  in  a 

Fig.  204.     Larva  of  yellow  fever    dry    place,    thoUgh    capable    of    Hv- 

mosquito,    Aedes    caiopus.     X  10.  jjjg    nearly    two    weeks    on    moist 

(After  Howard,  Dyar  and  Knab.)  , 

ground. 
The  pupae  (Fig.  205)  transform,  under  normal  conditions,  in  a 
day  and  a  half  or  two  days.  The  entire  cycle  from  egg  to  adult 
seldom  takes  place  in  less  than  nine  or  ten  days,  and  probably 
12  or  15  days  is  more  usual  under  ordinary  conditions.  As  has 
been  shown  above,  the  period  of  development  may  be  drawn  out 
over  several  months  by  unfavorable  conditions.  The  adult  mos- 
quitoes may  live  for  a  considerable  time,  and  apparently  are 
able  to  transmit  yellow  fever  any  time  from  12  days  after  in- 
fection to  the  end  of  their  lives.     Male  mosquitoes  ordinarily 


HABITS  OF  AEDES  CALOPUS 


447 


will  not  live  beyond  50  days,  but  the  females  frequently  live 
under  laboratory  conditions  for  four  months  or  more.  Kind 
of  food,  dryness  of  climate  and  facilities  for  laying  eggs  are  among 
the  chief  factors  determining  the  length  of  life  of  these  mosquitoes, 
and,  strange  as  it  appears  at  first, 
the  length  of  life  is  shortest  under 
the  most  favorable  conditions, 
namely,  plenty  of  blood  for  food, 
plenty  of  moisture,  and  suitable 
places  for  egg-laying. 

The  flight  of  the  yellow  fever 
mosquito  is  strong  but,  Uke  most 
other  mosquitoes,  it  seldom  flies 
long  distances,  usually  not  more 
than  a  few  hundred  feet.  Vessels 
lying  half  a  mile  from  shore  rarely 
if  ever  are  visited  by  these  mosqui- 
toes unless  the  latter  are  carried 

from  shore  by  lighters  or  boats.  Fm.    205.      Pupa   of   yellow   fever 

Owing   to  its   domestic  habits  gra^drblfatrXabf  "^  '^'" 
and  its  ability  to  ''  stow  away  " 

the  yellow  fever  mosquito  has  been,  and  annually  is,  widely 
distributed  over  the  world.  As  pointed  out  by  Howard,  Dyar  and 
Knab,  its  original  home  was  very  probably  tropical  America, 
since  the  evidence  points  to  the  origin  of  yellow  fever  in  the 
West  Indies  and  neighboring  mainland,  and  it  is  inconceivable 
that  the  parasite  of  this  disease  would  have  developed  in  any 
other  region  than  the  original  home  of  its  obligatory  host.  The 
permanent  home  of  this  mosquito  is  now  almost  the  entire  warm 
portion  of  the  world,  wherever  a  temperature  of  80°  or  more 
is  maintained  for  any  length  of  time,  and  where  freezing  does  not 
occur.  The  once  common  occurrence  and  breeding  of  this  mos- 
quito during  summer  months  in  cities  of  the  Atlantic  Coast  of 
the  United  States  and  in  other  ports  outside  the  frostless  zones  was 
due  to  its  importation  on  ships  from  such  infested  cities  as  New 
Orleans,  Havana  and  Rio  de  Janeiro.  The  cool  nights  and  low 
summer  temperatures  on  the  Pacific  Coast  of  the  United  States 
prevents  its  thriving  there,  in  spite  of  the  fact  that  it  is  still  some- 
times carried  there  on  ships.  Since  the  practical  extermination 
of  this  mosquito  in  most  of  the  ports  where  it  was  once  abundant 


448  MOSQUITOES 

its  importation  to  other  places  has  become  a  rare  occurrence. 
Since  Aedes  calopus  has  a  much  wider  range  than  has  yellow  fever 
there  is  constant  danger  of  the  introduction  of  the  disease  into 
places  where  it  has  not  previously  been  known  and  where,  due 
to  the  non-immune  condition  of  the  people,  it  would  become 
a  terrible  scourge  if  once  successfully  introduced.  For  this 
reason  the  yellow  fever  mosquito  is  fought  as  a  public  menace 
in  India,  Australia  and  many  of  the  South  Sea  Islands,  where  it 
is  frequently  the  most  abundant  mosquito. 

Mosquitoes  and  Dengue 

The  relation  of  mosquitoes  to  dengue  or  breakbone  fever  was 
first  pointed  out  by  Graham,  of  Beirut,  in  1902,  who  performed 
experiments  which  showed  that  this  disease  was  not  caught  by 
close  association  with  patients  in  the  absence  of  mosquitoes, 
whereas  isolated  men  subjected  to  bites  from  mosquitoes  which 
had  bitten  dengue  patients  readily  contracted  the  disease. 
Other  workers  have  adduced  evidence  in  favor  of  the  mosquito 
transmission  of  the  disease,  and  Ashburn  and  Craig  in  the  Philip- 
pines have  shown  that  laboratory-bred  mosquitoes,  fed  on  dengue 
patients,  could  transmit  the  disease  three  days  after  the  infective 
meal.  The  nature  of  the  disease  and  development  of  it  in  mos- 
quitoes and  man  is  discussed  in  Chap.  X,  pp.  186-187.  It  is  a 
disease  which  resembles  a  mild  form  of  yellow  fever,  is  seldom  fatal, 
and  occurs  in  very  sweeping  and  rapidly  traveling  epidemics. 

Transmitting  Species.  The  tropical  house  mosquito,  Culex 
quinquefasciatus  (fatigans)  and  Aedes  calopus  have  been  shown 
to  be  the  principal  transmitters  of  dengue.  Circumstantial  evi- 
dence, such  as  distribution  and  epidemiology  of  the  disease, 
habits  of  the  mosquitoes,  etc.,  all  point  to  C  quinquefasciatus  as 
being  the  most  important  species  concerned.  Aedes  calopus  has 
repeatedly  been  suspected  of  transmitting  the  disease,  especially 
in  Australia,  but  conclusive  evidence  of  this  has  been  brought 
forth  only  recently.  A  species  closely  related  to  Aedes  calopus, 
Desvoidea  ohturhanSj  has  been  iacriminated  in  Formosa. 

C.  quinquefasciatus  is  the  common  house  mosquito  of  the 
tropics,  and  very  closely  resembles  the  house  mosquito  of  tem- 
perate climates,  C.  pipiens,  in  both  appearance  and  habits.  It 
is  brown  in  color  with  a  broad  whitish  band  on  each  abdominal 


MOSQUITOES  AND  FILARIA  449 

segment.  The  thorax  and  legs  are  plain  brown  except  for  a  pale 
area  at  the  bases  of  the  legs. 

This  species  is  very  common  in  houses  in  all  thickly  populated 
parts  of  tropical  and  subtropical  portions  of  the  world,  though 
not  so  thoroughly  '^  domestic  "  as  Aedes  calopus.  In  America 
it  becomes  abundant  in  summer  as  far  north  as  Washington  and 
St.  Louis.  It  is  strictly  nocturnal  and  will  bite  in  complete 
darkness,  therefore  its  work  supplements  that  of  the  yellow  fever 
mosquito,  the  latter  taking  the  day  shift,  the  former  the  night 
shift.  The  house  mosquito  does  not  pursue  man  with  as  much 
devilish  cunning  and  perseverance  as  does  Aedes  calopus,  and, 
indeed,  shows  a  very  inferior  grade  of  intelligence  as  compared 
with  it.  There  is  reason  to  believe  that  it  is  primarily  a  perse- 
cutor of  birds  and  poultry,  and  attacks  man  only  as  a  second 
choice.  C.  quinquefasciatus  breeds  in  almost  any  standing  water 
but  apparently  prefers  artificial  receptacles  and  is  partial  to  filthy 
water.  The  eggs,  about  200  to  300  in  number,  are  laid  in  rafts 
as  is  the  case  with  other  members  of  the  genus.  The  larvae 
(Fig.  196A),  which  hatch  in  from  one  to  three  days,  have  long 
breathing  tubes,  and  feed  chiefly  on  microscopic  organisms. 
The  length  of  time  required  for  the  mosquitoes  to  reach  the  adult 
stage  from  the  time  the  eggs  are  laid  depends  very  largely  on 
temperature,  food  conditions,  etc.  The  minimum  period  is 
probably  about  five  or  six  days. 

Alcock  remarks  about  this  mosquito:  ''Apart  from  its  prac- 
tical importance,  Culex  fatigans  (or  Culex  quinquefasciatus)  has 
a  peculiar  interest  as  being  the  living  document  of  two  discoveries 
of  the  first  magnitude  in  the  history  of  medicine,  namely,  Sir 
Patrick  Hanson's  discovery  ...  of  the  part  played  by  mos- 
quitoes in  the  Ufe  cycle  of  certain  filarial  blood-parasites,  and 
Sir  Ronald  Ross's  discovery  ...  of  the  necessary  connection 
between  mosquitoes  and  certain  Protozoon  blood-parasites.  The 
first  discovery  laid  open  a  new  world  to  Pathology;  the  second, 
which  is  the  outcome  of  the  first,  will  affect  the  destiny  of  the 
human  race." 

Mosquitoes  and  Filaria 

As  intimated  in  the  last  paragraph  above,  the  discovery  by 
Sir  Patrick  Manson  in  1879  of  the  function  of  the  mosquito  as 
an  intermediate  host  of  filarial  worms,  the  larvse  of  which  live 


450  MOSQUITOES 

in  the  blood,  marked  the  beginning  of  a  new  era  in  medical 
science;  it  was  the  first  evidence  of  the  development  of  germs 
of  human  disease  in  the  bodies  of  insects.  An  account  of  the 
life  cycle  of  filarial  worms,  including  the  development  in  the 
bodies  of  mosquitoes,  the  means  by  which  the  worms  are  re- 
turned to  their  primary  hosts,  and  the  effect  of  filarial  infection 
on  man,  will  be  found  in  Chap.  XVII,  pp.  299-306. 

Not  all  species  of  filarial  worms  utilize  mosquitoes  as  inter- 
mediate hosts,  a  notable  exception  being  the  loa  worm  of  Africa. 
Four  human  species,  Filaria  bancrofti,  F.  philippinensis,  F.  per- 
stans  and  F.  juncea  (demarquayi)  are  known,  or  thought,  to  be 
nursed  by  mosquitoes.  The  last  two  named  are  not  known  to 
have  any  pathogenic  effects,  but  F.  bancrofti  is  connected  either 
directly  or  indirectly  with  a  number  of  human  ailments  (see 
p.  306).  F.  philippinensis  is  closely  allied  to  F.  bancrofti,  but 
differs  in  that  it  appears  in  the  peripheral  blood  diurnally  as  well 
as  nocturnally,  a  habit  which  is  supposed  to  be  associated  with 
the  diurnal  habits  of  its  usual  intermediate  host,  Aedes  pseudo- 
scutellaris. 

Although  the  successful  development  of  filarial  worms  is  not 
limited  to  one  particular  species  of  mosquito  or  even  to  any 
particular  group  of  species,  the  development  is  not  completed 
equally  well  in  all  species.  The  tropical  house  mosquito,  Culex 
quinquefasciatus,  is  the  species  in  which  the  worms  apparently 
develop  most  frequently  with  least  fatality  to  either  worms  or 
mosquitoes.  In  Fiji  the  development  of  the  worms  is  more 
regular  and  more  rapid  in  A  edes  pseudoscutellaris  than  in  any  other 
mosquito.  In  Aedes  calopus,  however,  the  development  of  the 
worms  is  very  slow,  and  they  eventually  degenerate  in  the  tho- 
racic muscles  without  reaching  maturity.  Many  species  of 
Anopheles  serve  as  suitable  hosts,  as  do  also  some  species  of 
Mansonia  and  other  genera.  In  many  species  of  mosquitoes 
the  filarial  larvse  are  digested,  or  else  die  in  the  course  of  their 
development.  On  the  other  hand,  there  are  some  mosquitoes 
which  are  very  susceptible  to  the  injury  done  by  the  worms, 
especially  in  case  of  heavy  infestation,  and  the  mortality  may 
amount  to  a  large  per  cent.  Apparently  the  most  critical  time 
for  the  mosquitoes  is  when  the  larvae  have  penetrated  into  the 
proboscis.  This  is  a  striking  example  of  the  almost  universal 
truth  in  parasitology,  that  the  host  in  which  the  asexual  cycle  of  a 


MOSQUITOES  AND   DERMATOBIA  451 

parasite  is  passed  is  less  perfectly  immune  to  the  parasite,  and 
the  parasite  less  perfectly  adapted  to  the  host,  than  is  the  case 
between  a  parasite  and  the  host  in  which  it  goes  through  the 
mature  sexual  phase  of  its  life  history.  In  the  case  in  hand 
man  may  be  looked  upon  as  the  disseminator  of  a  deadly  disease 
among  mosquitoes  in  much  the  same  way  that  the  mosquito 
may  be  considered  the  disseminator  of  deadly  human  diseases 
in  the  case  of  malaria  and  yellow  fever. 

Mosquitoes  and  Dermatohia 

In  many  parts  of  tropical  America  where  the  man-infesting 
botfly,  Dermatohia  hominis  (see  Chap.  XXVII,  pp.  513-515),  is 
found  there  has  long  been  a  belief  among  the  natives  that  the 
maggots  of  this  fly,  which  develop  under  the  skin  of  man  and  of 
many  other  animals,  are  in  some  way  the  result  of  mosquito  bites. 
Inhabitants  of  some  endemic  regions,  e.g.,  Trinidad,  point  to 
mosquitoes  as  the  cause  of  the  skin  maggots,  and  in  some  places 
the  larvae  are  known  as  "  mosquito-worms."  Until  recently 
the  scientific  world  looked  upon  these  beliefs  as  mere  superstition, 
and  gave  them  no  further  thought.  In  1911,  however.  Dr. 
Morales,  of  Guatemala,  received  a  specimen  of  a  mosquito  sent 
him  as  a  mosquito  ''  carrier  "  of  Dermatohia,  with  eight  relatively 
large  elliptical  eggs  glued  by  their  posterior  ends  to  its  abdomen. 
A  few  days  later  a  larva  emerged  from  one  of  the  eggs,  and  was 
induced  to  enter  an  abrasion  in  the  skin  of  an  attendant,  where 
it  thrived  so  well  that  for  the  patient's  sake  it  was  removed  after 
a  little  over  six  weeks  and  transplanted  to  the  back  of  a  rabbit. 
Here  it  continued  its  development  and  escaped,  probably  just 
before  pupation,  exactly  two  months  after  the  eggs  were  first 
received.  Dr.  Morales  was  quite  certain  that  the  larva  was 
really  a  Dermatohia.  In  the  same  year  Dr.  Tovar  of  Caracas, 
Venezuela,  made  similar  discoveries,  and  is  said  to  have  caused 
typical  Dermatohia  tumors  by  allowing  an  egg-laden  mosquito 
to  bite  a  susceptible  animal.  From  these  tumors  the  larvae 
were  obtained  at  the  end  of  11  days  and  from  these  larvae  the 
adult  flies  were  reared.  Dr.  Surcouf  of  Paris,  Dr.  Knab  of  the 
United  States,  and  Dr.  Sambon  of  England  have  published  ob- 
servations of  their  own  bearing  on  the  r61e  of  the  mosquito  in 
transmitting  Dermatohia  infection.  From  these  observations 
one  would  be  inclined  to  believe  that,  as  expressed  by  Dr.  Rin- 


•452  MOSQUITOES 

cones  of  Caracas,  the  mosquito  is  utilized  by  the  Dermatohia  fly 
as  an  aeroplane  for  transporting  her  eggs  or  larvae  to  a  suitable 
host  for  development,  and  we  would  have  here,  if  true,  one  of 
the  strangest  interrelations  of  animals  in  the  whole  realm  of 
nature,  comparable,  perhaps,  with  the  manner  in  which  certain 
mites  of  the  family  Tyroglyphidse  assume  a  special  traveling  garb 
and  adhere  to  the  appendages  of  flies  to  obtain  transportation 
to  new  feeding  grounds  (see  pp.  339-340). 

Dr.  Neiva,  of  the  Instituto  Oswaldo  Cruz,  at  first  did  not 
believe  in  the  mosquito  theory.  He  pointed  out  that  in  various 
parts  of  tropical  America  not  only  mosquitoes,  but  also  craneflies, 
ichneumon-flies,  certain  large  hairy  flies  and  other  insects  are 
accused  of  being  Dermatohia  carriers,  though  they  could  not 
possibly  serve  in  this  capacity.  It  is  known  now,  however,  that 
various  species  of  flies  as  well  as  the  mosquitoes  are  used  by 
Dermatohia,  and  it  would  be  expected  that  at  times  a  fly,  impelled 
by  the  urgent  desire  to  oviposit,  might  be  content  to  deposit  her 
eggs  on  insects  which  could  not  very  well  serve  the  purpose  of 
transporting  the  eggs  to  a  suitable  host.  Neiva,  when  he  ob- 
jected to  the  mosquito  theory,  had  not  found  any  egg-carrying 
mosquitoes  in  Brazil,  where  Dermatohia  is  common,  but  in  a  later 
publication  he  records  not  only  Janthinosoma  lutzi,  the  mosquito 
incriminated  in  Venezuela  and  Central  America,  as  an  egg-carrier, 
but  also  another  species  of  Janthinosoma,  J.  posticata,  and  several 
kinds  of  muscid  flies  (see  p.  514).  He  also  found  on  dissection  of 
female  Dermatohia  flies,  that  the  eggs  were  in  various  stages  of 
development  and  thought  this  argued  against  the  utilization  of 
mosquitoes  as  carriers,  but  it  has  subsequently  been  shown  by 
Neiva  himself  that  the  eggs  are  laid  in  small  groups  on  captured 
insects,  and  by  no  means  all  at  one  time.  Dermatohia  is  fre- 
quently found  pestering  cattle  and  horses,  and  egg-containing 
females  sometimes  persistently  follow  human  beings.  It  is  not 
certain  that  the  fly  does  not  sometimes  deposit  its  eggs  directly 
on  the  skin  of  the  host  in  which  the  larvae  are  to  develop,  but  its 
presence  near  large  animals  may  be  due  to  its  pursuit  of  other 
insects  which  swarm  around  them. 

There  is  no  doubt  any  longer  but  that  the  widespread  popular 
belief  in  the  part  played  by  the  mosquito  is  founded  on  fact. 
Insects  carrying  eggs  of  the  fly  have  repeatedly  been  found,  and 


MOSQUITO   BITES  AND   REMEDIES 


453 


the  females  have  been  observed  holding  other  flies  between  their 
legs,  and  in  captivity  have  been  observed  to  deposit  their  eggs 
on  various  species  of  flies.  As  remarked  by  Sambon,  this  fly  may 
have  several  ways  of  disposing  of  its  eggs,  but  the  utilization  of 
the  mosquito  and  other  insects  as  transports  for  them  is  probably 
the  usual  method. 

The  mosquito  involved  is  most  frequently  found  to  be  a  species 
of  Janthinosoma.  In 
Central  America  J. 
lutzi  alone  has  been  in- 
criminated, but  in  Sao 
Paulo,  Brazil,  this  spe- 
cies and  J.  posticata, 
and  also  other  mos- 
quitoes, have  been 
found  to  transport  Der- 
matohia  eggs.  J.  lutzi 
(Fig.  206)  is  a  large 
and  beautifully  colored 
mosquito,  with  flashes 
of  metallic  violet  and 
sky  blue  on  its  thorax 
and  abdomen.        It  is 

.,  1       j^      ,     ,      r  Fig.    206.      Mosquito,    Janthinosoma  lutzi,    with 

SaiCl  Dy  JYnaD  to  De  one  eggs,  supposedly  of  Dermatobia  hominis,  attached 
of      the      most       blood-  to  abdomen.     (After  Sambon.) 

thirsty     of     American 

mosquitoes  and  is  found  throughout  tropical  America.  The 
larvae  breed  almost  exclusively  in  rain  puddles,  the  eggs  being 
laid  in  dry  depressions  on  the  forest  floor  which  will  become  basins 
of  water  after  a  tropical  down^^our  of  rain.  The  eggs  hatch  almost 
with  the  first  drop  of  rain,  and  mature  so  rapidly  that  adult  in- 
sects may  emerge  in  four  or  five  days.  The  larvae  feed  on  par- 
ticles of  organic  matter,  and  are  themselves  fed  upon  by  the 
larvae  of  the  closely  allied  genus  of  mosquitoes,  Psorophora,  which 
breed  in  the  same  rain  pools. 


Mosqtiito  Bites  and  Remedies  for  Them 

As  has  been  remarked  before,  the  pain  and  irritation  produced 
by  a  mosquito  bite  is  usually  believed  to  be  due  to  the  injection 


454  MOSQUITOES 

of  a  bit  of  poisonous  saKva  into  the  wound  made  by  the  piercing 
mouthparts  of  the  insect.  The  susceptibiUty  of  some  people  to 
the  effect  of  mosquito  poison  is  much  greater  than  that  of  others. 
The  author  has  seen  individuals  on  whom  mosquito  bites  swelled 
up  like  bee  stings  and  were  even  more  painful,  whereas  the  author 
himself  has  frequently  been  unaware  of  the  fact  that  a  mosquito 
was  biting  him  unless  the  insect  was  seen  by  him  or  was  pointed 
out  by  a  less  indifferent  companion.  Moreover,  the  effect  of  the 
bites  of  different  species  of  mosquitoes  varies,  so  that  while  some 
species  may  produce  very  little  irritation  others  may  prove  un- 
bearably annoying.  Dr.  Smith,  of  New  Jersey,  became  prac- 
tically immune  to  the  bites  of  some  of  the  salt  marsh  mosquitoes, 
but  was  troubled  by  the  house  mosquito,  Culex  pipiens,  and  still 
more  so  by  Anopheles.  The  author  has  had  similar  experience, 
and  has  found  himself  driven  almost  to  frenzy  by  some  species 
and  hardly  annoyed  at  all  by  others.  It  is  quite  probable  that 
the  complaints  which  are  heard  from  visitors  to  the  ocean  resorts 
of  the  New  Jersey  coast  are  due  to  the  fact  that  these  visitors 
are  fully  susceptible  to  the  poison  of  the  salt  marsh  mosquitoes 
whereas  they  may  have  become  more  or  less  immune  to  the 
inland  mosquitoes  of  their  own  districts.  These  facts  clearly 
indicate  that  there  is  a  specific  difference  in  the  poison  of  different 
kinds  of  mosquitoes,  and  Dr.  Smith's  experiences  show  that 
acquired  immunity  to  one  mosquito  may  give  little  or  no  relief 
from  another. 

There  is  a  popular  belief  that  if  a  mosquito  is  allowed  to  draw 
his  fill  of  blood,  the  bite  is  less  painful  and  becomes  less  swollen 
than  if  she  is  killed  or  driven  away.  This  belief  is  to  a  large 
extent  true,  the  probable  reason  being  that  when  the  insect 
is  allowed  to  finish  her  meal,  the  droplet  of  poisonous  saliva  in- 
jected into  the  Wound  is  drawn  back  into  the  stomach  of  the 
mosquito  with  the  blood  on  which  it  acts. 

Many  different  remedies  have  been  recommended  for  mos- 
quito bites.  Ammonia,  alcohol,  glycerine,  indigo,  iodine,  ether, 
camphor,  naphthaline  (moth  balls),  cresol  preparations,  a  2 J 
per  cent  carbolic  solution  —  all  these  and  others  have  had  their 
adherents  amongst  entomologists,  hunters,  travelers  and  house- 
wives. All  of  them  probably  have  some  alleviating  effect,  and 
it  is  not  unlikely  that  their  effects  may  vary  with  different  spe- 
cies  of   mosquitoes   and   perhaps   even   with   individuals.     Dr. 


PERSONAL  PROTECTION  455 

Howard  found  that  moist  soap  rubbed  on  the  bites  was  the  most 
satisfactory  remedy  in  his  own  personal  experience. 

Probably  no  remedy  or  disinfectant,  no  matter  how  quickly 
applied  after  an  infected  mosquito  has  been  sucking  blood,  would 
be  effective  in  preventing  infection  with  malaria,  yellow  fever 
or  dengue.  Filaria  and  Dermatohia  infections,  however,  could 
probably  be  prevented  in  this  manner,  since  it  takes  an  ap- 
preciable time  for  the  larvae  to  enter  the  skin  in  the  vicinity  of  the 
wound. 

Control  and  Extermination 

The  control  of  mosquitoes  may  be  undertaken  in  the  following 
ways,  in  order  of  permanent  usefulness:  (1)  personal  protection 
by  the  use  of  repellents  on  or  near  the  person,  or  of  protective 
clothing;  (2)  the  elimination  and  exclusion  of  mosquitoes  from 
dwellings;  (3)  the  local  destruction  of  larvae  by  the  use  of 
temporary  'Marvicides ";  (4)  the  prevention  of  breeding  by 
obliterating  breeding  places  or  making  them  uninhabitable. 

Personal  Protection.  —  This  method  of  dealing  with  mos- 
quitoes has  no  permanent  value  whatever,  and  does  nothing  to 
lessen  the  number  of  mosquitoes,  but  it  is  indispensible  to  the 
hunter  or  visitor  in  mosquito-infested  places.  Concerning  the 
use  of  protective  clothing,  little  need  be  said;  the  value  of  gloves, 
veils,  high  boots,  leggings,  etc.,  is  obvious. 

The  use  of  "  mosquito  dope,"  or  ointments  repellent  to  mos- 
quitoes, on  the  exposed  skin  is  a  popular  but  usually  disappoint- 
ing safeguard  against  attacks  by  these  insects.  The  number  of 
popular  repellents  for  mosquitoes  is  as  great,  if  not  greater,  than 
the  number  of  popular  applications  for  the  bites.  Nearly  all 
of  these  are  unquestionably  effective  while  they  last,  but  they 
all  have  the  disadvantage  of  losing  their  power  by  evaporation 
in  a  short  time,  and  therefore  have  to  be  renewed  at  frequent 
intervals.  Spirits  of  camphor,  oil  of  pennyroyal,  oil  of  pepper- 
mint, lemon  juice,  vinegar,  anise  oil  and  oil  of  citronella  are 
all  effective  protectors  while  they  last.  Oil  of  citronella  has 
been  most  widely  used  in  America.  This  mixed  with  an  equal 
amount  by  weight  of  spirits  of  camphor  and  half  as  much  oil  of 
cedar  is  a  mixture  recommended  by  Dr.  Howard,  and  one  which 
the  author  has  used  with  good  results.  A  few  drops  of  this  mix- 
ture poured  on  a  bath  towel  at  the  head  of  a  bed,  and  a  little 


456  MOSQUITOES 

rubbed  on  the  face  and  hands  if  the  mosquitoes  are  very  per- 
sistent, was  found  by  Dr.  Howard  to  last  long  enough  through 
the  night  to  be  effective  against  all  mosquitoes  except  the  yellow 
fever  species,  Aedes  calopus,  which  begins  its  attacks  at  daybreak. 

Elimination  and  Exclusion  from  Buildings.  —  The  second 
means  of  controlling  mosquitoes,  by  eUminating  and  excluding 
them  from  dwellings,  is  of  more  permanent  value  than  the  first, 
and  should  never  be  omitted  while  the  process  of  mosquito 
extermination  is  under  way. 

One  of  the  best  methods  of  ridding  houses  of  mosquitoes  after 
they  are  once  in  is  fumigation,  and  this  is  also  an  indispensable 
method  of  destroying  hibernating  mosquitoes  in  cellars,  attics, 
barns,  etc.  The  substance  used  for  fumigation  must  depend  on 
the  kind  of  place  to  be  fumigated,  and  on  the  conditions  under 
which  it  is  done.  The  most  thorough  and  certain  method  of 
fumigation,  when  the  place  to  be  fumigated  can  be  vacated,  is 
by  the  generation  of  hydrocyanic  acid  gas.  A  less  dangerous 
and  equally  effective  method,  but  one  which  is  injurious  to  metals 
and  house  furnishings  is  by  the  use  of  fumes  of  burning  sulphur. 
These  methods  of  fumigation  are  described  in  Chap.  XXII,  pp. 
383-386. 

Fumigants  which  are  not  dangerous  to  human  beings  can  be 
used  effectively  against  mosquitoes  since  these  insects  do  not 
require  such  penetrating  fumes  as  are  necessary  to  destroy 
hiding  parasites,  as  bedbugs  and  lice.  Pyrethrum  or  Persian 
insect  powder,  manufactured  out  of  the  dried  flower  heads  of 
certain  species  of  chrysanthemums,  is  an  effective  fumigant  of 
this  type;  it  can  either  be  dusted  into  corners,  blown  into  the 
air  of  a  room,  or  burned.  Powdered  jimson  weed,  Datura 
stramonium,  is  recommended  by  Dr.  Smith,  eight  ounces,  mixed 
with  one-third  its  weight  of  niter  or  saltpeter  to  make  it  burn 
more  readily,  being  burned  per  1000  cubic  feet.  "  Mimm's 
Culicide  "  is  a  volatile  liquid  made  of  carbolic  acid  crystals  and 
gum  camphor  in  equal  parts  by  weight,  which  is  effective  against 
mosquitoes,  four  ounces  being  volatilized  by  heating  for  every 
1000  cubic  feet  of  space.  A  fumigant  which  has  come  into  great 
favor  in  the  last  few  years  is  cresyl;  75  grains  to  35  cubic  feet  is 
sufficient  to  kill  all  mosquitoes,  and  in  this  dilution  it  is  not  in- 
jurious to  man  or  other  higher  animals.  It  is  not  injurious 
to  metals  or  to  household  goods. 


ELIMINATION  FROM   BUILDINGS  457 

In  camps  which  are  not  mosquito  proof,  the  only  effective 
means  of  obtaining  comfort  is  by  the  use  of  smudges  as  described 
for  blackflies  (p.  484). 

Protection  of  houses  against  mosquitoes  is  almost  a  necessity 
in  many  places.  To  a  certain  extent  the  construction  of  a  house 
affects  the  number  of  mosquitoes  attracted  to  it.  Light,  airy 
rooms  with  white  walls  are  much  less  infested  with  mosquitoes 
than  are  dark,  damp  houses.  Ross  says  that  houses  decorated 
with  curtains,  pictures,  stuffed  chairs  and  similar  "  barbarous  '* 
furnishings  are  entirely  inappropriate  for  the  tropics,  and  he 
deplores  especially  the  use  of  curtains  since  they  "  check  the 
breeze  which  is  so  cooling  to  the  inmates  and  so  unpleasant  for 
mosquitoes." 

The  careful  screening  of  houses  or  rooms  is  highly  valuable, 
especially  in  places  where  mosquito-borne  diseases  are  prevalent. 
Mosquito  net  or  screen  should  never  be  less  than  18  meshes  to 
the  inch.  Cloth  net  is  more  effective  than  wire,  since  mos- 
quitoes cannot  as  readily  force  their  way  through,  but  nets  with 
thin  threads  should  be  used  and  should  be  stretched  tightly  in 
order  not  to  exclude  the  breeze  in  hot  weather.  The  use  of  tight 
canopies  over  beds  is  extensively  practiced  in  southern  United 
States,  especially  in  malarial  districts,  and  these  are  very  com- 
mendable when  kept  in  good  repair.  Most  firms  dealing  in  camp 
outfits  place  on  the  market  light  folding  frames  covered  with 
mosquito  netting  for  use  when  resting  or  sleeping  out  of  doors 
in  mosquito-infested  places. 

Usually  a  few  mosquitoes  find  their  way  into  screened  rooms 
in  spite  of  the  screens,  through  unnoticed  crevices,  opening  of 
doors  and  the  like.  These  can  usually  be  discovered  and  des- 
troyed with  a  fly  spanker,  or,  what  is  just  as  effective  in  case 
spotting  the  walls  with  blood  is  to  be  avoided,  by  holding  a  cup 
of  kerosene  directly  under  them.  The  mosquitoes  are  stunned 
by  the  vapor  and  fall  into  the  cup  in  a  few  seconds.  Mosquito 
traps  have  been  found  useful  in  some  places,  these  contrivances 
consisting  merely  of  a  box,  dark  colored  inside,  placed  where  it 
will  readily  be  found  by  mosquitoes  and  utilized  as  a  hiding 
place.  The  box  is  arranged  so  that  the  insects  do  not  readily 
find  their  way  out  and  so  that  it  can  be  fumigated  easily. 

Larvicides.  —  Far  more  effective  and  satisfactory  in  every 
way  as  a  method  of  coping  with  mosquitoes  is  their  actual  ex- 


458  MOSQUITOES 

termination,  not  necessarily  in  a  whole  continent  or  a  whole 
country,  but  in  local  places.  Only  comparatively  recently  has 
the  local  extermination  or  even  reduction  of  mosquitoes  ceased 
to  be  looked  upon  as  too  vast  an  operation  to  be  undertaken. 
Because  ponds  or  marshes  were  known  to  exist,  perhaps  miles 
away,  the  value  of  destruction  of  such  breeding  places  as  rain 
barrels,  tin  cans  full  of  water,  cesspools  and  troughs  was  looked 
upon  as  a  mere  drop  in  the  bucket.  Knowing  as  we  do  now  that 
in  most  cases  every  annoying  mosquito  which  attacks  us  was 
born  and  bred  within  200  yards  of  where  we  meet  her,  the 
local  extermination  of  mosquitoes  has  taken  on  a  very  different 
aspect.  It  is  difficult  for  the  uninitiated  to  realize  that  the 
mosquitoes  which  make  life  miserable  for  him  did  not  travel  from 
distant  marshes  and  ponds  but  were  probably  bred  in  his  own 
backyard  or  in  his  own  living  room. 

Wonderful  results  have  been  obtained  by  the  destruction  of 
larvae  in  their  breeding  places.  This  is  accomplished  either  by 
pouring  into  the  water  some  substance  which  will  form  an  emul- 
sion, and  will  destroy  the  larvae  when  very  dilute,  or  by  pouring  or 
spraying  some  oil  on  the  water  which  will  spread  out  and  form 
a  thin  film  over  the  whole  surface.  When  the  larvae  rise  to  obtain 
air  through  their  breathing  tubes  or  pores,  the  latter  become 
plugged  by  a  tiny  bit  of  oil,  and  the  larvae  drown.  It  has  recently 
been  pointed  out  by  Lima,  in  Brazil,  that  the  drowning  is  has- 
tened by  the  coating  of  the  body  of  the  larvae  by  the  oil,  especially 
in  Anopheles,  so  that  air  cannot  be  absorbed  through  the  body 
wall. 

The  oil  film  is  the  method  most  commonly  employed,  espe- 
cially for  use  on  a  small  scale.  Except  for  wind-swept  bodies  of 
water,  ordinary  petroleum  is  as  cheap  and  efficient  as  any  oil 
that  can  be  obtained.  The  oil  film  is  so  thin  and  light,  however, 
that  it  is  blown  aside  by  a  high  wind,  and  a  considerable  portion 
of  the  water  left  uncovered.  Different  grades  of  oil  can  be  used, 
varying  with  conditions.  The  thick  heavy  grades  do  not  readily 
form  a  uniform  film,  especially  if  obstructed  by  water  weeds, 
whereas  the  very  thin  oils  evaporate  rapidly,  and  the  film  is  easily 
broken.  Howard,  Dyar  and  Knab  recommend  a  grade  known 
as  "  light  fuel  oil  "  for  ordinary  use.  These  authors  state  that 
about  one  ounce  of  petroleum  to  15  square  feet  of  water  surface 
gives  satisfactory  results,  and  produces  a  film  which  lasts  for 


PREVENTION  OF  BREEDING  459 

ten  days.  Films  of  heavier  oils  or  heavy  and  light  oils  mixed 
last  longer,  and  need  be  renewed  only  once  in  two,  three  or  four 
weeks,  according  to  conditions.  Thin  oil  will  spread  into  a  film 
if  simply  poured  on  the  surface,  but  heavier  oils  are  best  sprayed 
on.  In  Africa  mops  made  by  tying  kerosene-soaked  cloths  on 
long  sticks  are  used  for  spreading  the  oil  and  in  Panama  waste 
cloth  soaked  in  oil  is  placed  where  a  slow  flowing  stream  will 
constantly  take  a  thin  film  from  it. 

In  the  tropics  the  use  of  petroleum  has  often  been  found  im- 
practicable on  account  of  the  rapid  evaporation,  continued 
heavy  rains,  and  the  interference  made  by  the  luxuriant  and 
rapid  growth  of  water  plants  and  algae  and  the  formation  of  an 
interfering  scum  from  a  combination  of  the  oil  and  dead  algae. 
For  this  reason  substances  which  are  actively  poisonous  to  the 
larvae  and  which  form  an  emulsion  in  the  water  are  used  instead. 
An  almost  ideal  larvicide  of  this  type  is  now  made  at  Ancon, 
C.  Z.,  in  enormous  quantities.  It  is  made  of  crude  carbolic  acid, 
powdered  resin  and  caustic  soda,  heated  together  to  make  a  black 
liquid  resin  soap  which  readily  forms  a  milky  emulsion  with 
water.  It  destroys  Anopheles  larvae  in  16  minutes  in  an  emul- 
sion of  one  part  in  5000.  It  also  kills  larvae  in  mud,  and  destroys 
grass,  algae  and  water  weeds  in  which  I'arvae  ordinarily  hide. 
Recently  cresol  has  been  advocated  as  a  larvicide,  dilutions  as 
low  as  one  part  per  million  being  said  to  be  fatal  in  a  short  time. 
Powdered  paraform  sprinkled  on  water  is  said  by  Roubaud  to  be 
specifically  fatal  to  mosquito  larvae. 

Prevention  of  Breeding,  and  Natural  Enemies.  —  The  most 
valuable  method  of  reducing  mosquitoes,  where  practicable,  is 
to  obliterate  breeding  places  or  to  make  them  uninhabitable 
for  the  larvae.  The  first  step  in  reducing  mosquitoes  is  to  see 
that  there  are  no  flower-vases  or  other  water  receptacles  serving 
as  aquaria  for  the  larvae,  that  there  are  no  water-filled  tin  cans 
in  the  garbage  heap  or  that  the  roof  or  street  gutters  do  not 
hold  standing  water.  Any  rain  barrels,  cisterns,  cesspools  or 
small  reservoirs  which  cannot  be  disposed  of  can  be  made  harm- 
less by  screening.  Pieces  of  low  ground,  temporary  pools,  etc., 
can  usually  be  eliminated  by  draining. 

The  natural  enemies  of  mosquito  larvae  can  often  be  exploited 
successfully  for  destroying  them.  Dr.  Smith  found  that  one  of 
the  most  potent  factors  in  the  reduction  of  mosquitoes  in  the 


460 


MOSQUITOES 


great  tidal  salt  marshes  of  the  New  Jersey  coast  were  the  various 
species  of  kilHfish.  These  fish  abound  wherever  the  marshes 
are  constantly  flooded  and  push  into  places  where  there  is  barely 
enough  water  to  cover  them,  and  are  so  active  in  destroying  mos- 


FiG.  207.  One  of  the  first  places  to  clean  up  in  a  mosquito  campaign.  A 
favorite  breeding  place  for  such  annoying  or  dangerous  species  as  the  yellow  fever 
mosquito,  Aedes  calopus,  the  house  mosquitoes,  Culex  pipiens  and  C.  quinquefas- 
ciatus,  Anopheles  quadrimaculatus,  and  others. 


quito  larv2e  that  the  latter  can  exist  only  in  high-lying  or  shut-in 
portions  of  the  marsh  over  which  the  tide  only  occasionally  sweeps 
and  to  which  the  ''  killies  "  do  not  penetrate.  Knowing  the 
value  of  killifish  as  destroyers  of  larvae,  the  problem  of  preventing 
the  marshes  from  producing  countless  mosquitoes  resolves  it- 
self into  so  draining  that  the  water  on  it  either  will  be  drawn 
off  at  every  low  tide  or  will  be  constantly  stocked  with  fish.  A 
number  of  workers  have  recently  remarked  on  the  folly  of  oiling 
pools  which  could  be  stocked  with  fish,  since  the  oil  kills  the 
natural  enemies  of  the  larvae  and  is  not  permanent.  Instead  it 
is  urged  that  fish  be  propagated  in  such  pools.  The  water  weeds, 
however,  should  be  removed  and  overhanging  plants  cut  back 
so  that  the  fish  can  operate  freely  in  their  pursuit  of  larvae.  In 
the  case  of  swamps  it  is  suggested  that  a  permanent  pond  be 
constructed  at  the  lowest  level  and  stocked  with  fish,  and  the 
swamp  drained  into  the  pond. 

A  fresh-water  fish  of  the  same  family  as  the  killifish  (Cyprino- 
dontidae)  known  as  ''  millions  "  {Girardinus  poeciloides)  has  been 


NATURAL  ENEMIES 


461 


found  very  efficient  as  a  destroyer  of  mosquito  larvae  and  has 
been  extensively  introduced  into  various  parts  of  the  tropics 
from  its  home  in  Barbados  and  other  West  Indian  Islands. 
Except  where  other  fish  are  present  to  prey  upon  it,  this  tiny 


Fig.  208.  Some  good  natural  enemies  of  mosquitoes;  A,  common  killifish, 
Fundulus  heteroclitus,  of  great  value  in  brackish  marshes;  B,  fresh-water  killifish, 
Fundulus  diaphanus,  valuable  in  fresh-water  streams  and  ponds.  |  nat.  size. 
(After  Jordan  and  Evermann.) 

fish  usually  thrives  wherever  introduced,  and  carries  with  it  a 
noticeable  diminution  in  mosquitoes.  Other  species  of  the  same 
family  occur  in  various  parts  of  the  world  and  are  almost  in- 
variably deadly  enemies  of  mosquito  larvae. 

Other  natural  enemies  of  the  larvae  besides  fish  might  well  be 
encouraged  in  ponds  or  reservoirs.  The  western  newt  or  water- 
dog,  Notophthalmus  (or  Diemyctylus)  torosus,  which  is  abundant  all 
along  the  Pacific  Coast  of  the  United  States,  has  been  observed 
to  feed  very  largely  on  larvae.  In  Oregon  the  author  has  ob- 
served grassy  pools,  which  were  otherwise  ideal  breeding  places 
for  mosquitoes  but  which  contained  numerous  water-dogs,  ab- 
solutely free  of  larvae,  whereas  other  pools  not  a  quarter  of  a 
mile  distant  in  which  no  newts  were  found  were  swarming  with 
larvae  and  pupae.  Recent  experiments  by  the  author  have 
demonstrated  conclusively  that  this  salamander  can  be  utilized 
successfully  to  keep  mosquito  larvae  out  of  such  receptacles  as 
rain  barrels,  troughs,  etc. 


462  MOSQUITOES 

Other  efficient  enemies  are  whirligig  beetles  (Gyrinidse),  pre- 
daceous  diving  beetles  and  various  aquatic  predaceous  larvae,  in- 
cluding some  species  of  mosquito  larvae.  Among  birds,  ducks 
have  been  quoted  as  efficient  destroyers  of  mosquitoes  and  Dixon 
of  Pennsylvania  recently  demonstrated  their  ability  to  keep  ponds 
free  of  larvae;  he  believes  the  mallard  duck  surpasses  any  other 
creature  in  the  number  of  mosquito  larvae  and  pupae  which  it  can 
destroy.  As  destroyers  of  adults  the  value  of  such  birds  as 
swifts,  nighthawks,  swallows,  etc.,  is  well  known.  Bats,  also, 
have  been  exploited  as  mosquito  destroyers.  The  erection  of 
"  bat  roosts  "  for  propagation  of  these  animals  has  been  tried  in 
Texas,  and  was  found  to  reduce  markedly  the  numbers  of  mos- 
quitoes, and  was  financially  profitable  on  account  of  the  guano 
which  could  be  collected. 


CHAPTER  XXVI 
OTHER  BLOOD-SUCKING  FLIES 

Importance.  —  Although  the  mosquitoes  hold  the  center  of 
the  stage  as  regards  importance  as  human  parasites,  there  are 
many  other  members  of  the  order  Diptera  which  affect  the  wel- 
fare of  the  human  race.  From  a  medical  point  of  view  the 
Diptera  are  far  more  important  than  all  other  arthropods  put 
together.  Besides  the  mosquitoes,  which  we  have  seen  are  the 
transmitters  of  at  least  four  and  probably  five  diseases,  two  of 
which  are  of  prime  importance,  the  Diptera  include  the  Phle- 
botomus  flies,  which  are  known  to  be  the  sole  disseminators  of 
phlebotomus  or  three-day  fever,  and  are  believed  to  be  the 
transmitters  of  verruga  in  Peru  and  of  oriental  sore  in  North 
Africa  and  possibly  other  places;  the  tsetse  flies,  which  are 
transmitters  and  intermediate  hosts  for  the  trypanosomes  of 
sleeping  sickness;  the  stable-fly  and  other  biting  allies  of  the 
housefly,  which  may  carry  the  bacteria  of  anthrax  and  other 
diseases  from  dead  or  dying  animals  to  human  beings;  the  gad- 
flies or  horseflies,  one  species  of  which  is  incriminated  as  the 
transmitter  of  the  African  loa  worm,  and  all  of  which  may  act 
in  the  same  capacity  as  stable-flies,  to  transmit  bacteria  mechani- 
cally from  the  blood  of  a  diseased  animal  to  a  healthy  animal 
or  person;  and  the  blackflies  (Simuliidse)  and  "  no-see-ums " 
(Chironomidse),  which  are  sometimes  terrible  pests  though  not 
known  to  be  disease  carriers.  Besides  these  blood-sucking 
species,  the  Diptera  include  also  all  the  insects  which  live  in  the 
human  body  as  maggots,  and  also  the  housefly  and  allied  species 
which,  though  not  properly  to  be  considered  parasites,  are 
nevertheless  of  incalculable  importance  as  mechanical  spreaders 
of  disease  germs. 

General  Structure  of  Diptera.  —  To  understand  the  relations 
of  these  numerous  important  insects  and  their  classification, 
we  must  make  a  brief  survey  of  the  characteristics  and  classi- 
fication of  the  order  Diptera.     The  whole  order  can  usually  be 

463 


464  OTHER  BLOOD-SUCKING  FLIES 

distinguished  readily  from  other  insects  by  the  fact  that  there 
is  only  one  pair  of  membranous  wings,  the  second  pair  of  wings 
being  represented  only  by  an  insignificant  pair  of  knobbed 
rodlike  appendages  known  as  halteres  (Fig.  191,  halt.).  The 
head  is  joined  to  the  thorax  by  a  very  slender  flexible  neck.  The 
thorax  itself  consists  of  one  mass  on  account  of  the  fusion  of  its 
three  component  parts,  and  the  abdomen  consists  of  from  four 
to  nine  visible  segments  and  is  terminated  by  the  ovipositors 
or  egg-laying  organs  in  the  female,  and  by  the  copulatory  organs 
in  the  male.  The  head  is  provided  with  a  pair  of  antennae,  a 
pair  of  maxillary  palpi  and  a  proboscis  composed  of  or  con- 
taining the  mouthparts.  The  antennae  and  also  the  palpi  are  of 
considerable  use  in  classification;  the  extent  of  the  variations  in 
the  antennae  may  be  gathered  from  Fig.  211.  The  mouthparts 
are  profoundly  modified  in  accordance  with  the  habits  of  the 
flies.  In  the  botflies,  in  which  the  adults  live  only  long  enough 
to  reproduce  their  kind,  the  mouthparts  and  even  the  mouth  are 
much  degenerated;  in  the  non-blood-sucking  forms,  such  as  the 
common  housefly,  the  mouthparts  are  more  or  less  fused  into  a 
fleshy  proboscis  which  is  used  for  lapping  up  dissolved  foods; 
in  the  blood-suckers,  which  are  the  forms  that  particularly  in- 
terest us  here,  the  mouthparts  are  developed  into  an  efficient 
sucking  and  piercing  apparatus.  In  some,  e.g.,  mosquitoes 
(Fig.  190)  and  horseflies  (Fig.  225),  the  lower  lip  acts  as  a  sheath 
for  the  other  parts  which  are  fitted  for  piercing  and  sucking; 
in  others,  e.g.,  the  stable-fly,  Stomoxys  (Fig.  240),  and  the  tsetse 
flies,  Glossina  (Fig.  229) ,  the  lower  lip  itself  forms  a  piercing  organ, 
and  the  epipharynx  and  hypopharynx  form  a  sucking  tube,  the 
mandibles  and  maxillae  being  absent. 

Life  Histories.  —  All  of  the  Diptera  have  a  complete  metamor- 
phosis (see  p.  329),  and  sometimes  undergo  a  most  profound 
remodeling  of  the  entire  body  during  the  usually  short  pupal 
stage.  The  life  history,  beyond  the  fact  that  a  complete  meta- 
morphosis occurs,  varies  within  very  wide  limits.  Most  flies  lay 
eggs,  but  some,  e.g.,  the  screw- worm  fly,  Cochliomyia  (or  Chryso- 
myia),  and  allied  species,  produce  newly  hatched  larvae  or  eggs 
which  are  just  at  the  point  of  hatching,  while  still  others,  e.g., 
the  tsetse  flies,  Glossina,  do  not  deposit  their  offspring  until  it 
has  undergone  its  whole  larval  development  and  is  ready  to 
pupate. 


LARV.E  AND  PUPiE  OF  DIPTERA 


465 


The  larvae  of  Diptera  may  be  simple  maggots  with  minute 
heads  and  no  appendages  and  capable  of  only  limited  squirm- 
ing movements,  e.g.,  the  screw- worms  (Fig.  250),  or  they  may 
be  quite  highly  developed,  active  creatures,  e.g.,  the  larvae  of 
mosquitoes,  midges,  etc.  Many  are  aquatic,  many  others  ter- 
restrial; usually  the  eggs  are  laid  in  situations  where  the  larvae 
will  find  conditions  suitable  for  their  development,  and  the  flies 
often  show  such  highly  developed  instincts  in  this  respect  that 
it  is  hard  not  to  credit  them  with  actual  forethought.  The 
pupae  of  the  Diptera  also  vary  widely.  In  one  great  suborder, 
Orthorrhapha,  the  pupa  is  protected  only  by  its  own  hardened 


Fig.  209.  Types  of  pupal 
cases,  showing  manner  of  emer- 
gence of  adults.  A,  empty  case 
of  blowfly,  typical  co-arctate 
pupa  of  Cyclorrhapha ;  B,  empty 
case  of  mosquito,  typical  ob- 
tected  pupa  of  Orthorrhapha. 


Fig.  210.  A,  fly  emerg- 
ing from  pupal  case,  show- 
ing bladder-like  ptilinium 
(ptil.)  by  means  of  which 
the  end  of  the  case  is 
pushed  off;  B,  face  of  fly 
showing  scar  or  lunule 
(lun.)  left  by  drying  up  of 
ptilinium.    (After  Alcock.) 


cuticle,  and  is  often  capable  of  considerable  activity;  from  this 
"  obtected  "  type  of  pupa  (Fig.  209B)  the  adult  insect  emerges 
through  a  longitudinal  sht  along  the  back.  In  the  other  sub- 
order, Cyclorrhapha,  the  pupa  retains  the  hardened  skin  of  the 
larva  as  a  protective  covering  or  "  puparium,"  and  is  usually 
capable  of  very  slight  movement;  from  this  "  co-arctate  "  type 
of  pupa  (Fig.  209A)  the  adult  escapes  by  pushing  off  the  anterior 
end  of  the  puparium  with  a  hernia-like  outgrowth  on  the  front  of 
the  head.  This  outgrowth,  called  the  ''  ptiUnium  "  (Fig.  210A), 
shrinks  after  the  fly  has  emerged,  but  leaves  a  permanent  cres- 
cent-shaped mark  on  the  head  known  as  the  "  frontal  lunule  " 
(Fig.  21  OB)  which  embraces  the  bases  of  the  antennae,  and  gives 


466  OTHER  BLOOD-SUCKING  FLIES 

a  dependable  clue  to  the  early  life  of  the  insect.  Adult  flies  are 
usually  not  long  lived,  and  often  live  only  a  few  days,  just  long 
enough  to  copulate  and  lay  their  eggs.  Some  species,  however, 
e.g.,  mosquitoes,  may  live  for  several  months. 

The  order  Diptera,  as  already  indicated,  is 
j^^:^#^^%^  divided  into  two  great  suborders,  the  Orthor- 
y^jxaoax,  rhapha  and  the  Cyclorrhapha.     The  first  order 

,^^^__^  includes   those   species  which   have   a   well   de- 

P^^^^      C      veloped  larva  with  a  distinct  head,  and  an  ob- 
tected  type  of  pupa.     The  second  includes  the 
flies  which  have  headless  maggot-like  larvae  and 
D      a  coarctate  type  of  pupa.     In  nearly  all  of  these 
the  antennae  are  of  the  type  shown  in  Fig.  211D 
^      and  E.    These  suborders  are  further  divided  into 
t:.     c-,-,     rj.         sections  or  suborders  and  then  into  families,  but 

Fig.  211.    Types  ' 

of  antennae  of  Dip-  for  our  purposes  it  is  Unnecessary  to  follow  out 
female^'  T^ullk-  ^^^^  classification.  It  will  suffice  to  take  up, 
fly:  c,  gadfly  (tab-  family  by  family,  those  forms  which  are  impor- 
^""'stabfe-fly*'^^^'  *^^^  ^^  blood-sucking  parasites  of  man.  The 
mosquitoes  are  of  such  very  great  importance 
that  they  deserve  separate  consideration  and  have  been  discussed 
in  a  chapter  by  themselves  (Chap.  XXV). 


Phlebotomus  Flies 

General  Description.  —  Phlebotomus  flies,  otherwise  known 
as  ''  sandflies  "  or  "  owl-midges,"  are  minute  mothlike  midges 
which  are  found  in  nearly  all  warm  and  tropical  climates  of  the 
world,  with  the  exception  of  Australia  and  the  East  Indies.  In 
Australia  (Queensland)  they  are  represented  by  an  allied  fly 
of  the  same  family,  Pericoma  townsvillensis,  which  is  said  to  be 
a  very  severe  biter,  producing  swellings  which  may  last  three 
weeks.  They  belong  to  the  family  Psychodidae,  which  includes 
a  large  number  of  species  of  flies  found  all  over  the  world,  nearly 
all  of  which  resemble  tiny  moths  on  account  of  their  very  hairy 
bodies  and  mothlike  pose.  The  latter  characteristic,  however, 
is  not  shared  by  the  genus  Phlebotomus.  The  latter  is  the  only 
genus,  except  Pericoma,  containing  habitual  blood-suckers  with 
a  long  proboscis;  in  all  other  members  of  the  family  the  pro- 
boscis is  short  and  inconspicuous. 


PHLEBOTOMUS  FLIES  467 

The  phlebotomus  flies  (Fig.  212D)  are  small  dull-colored  in- 
sects, usually  yellowish  or  buff,  slender  in  build,  with  hairy 
body  and  very  long  and  lanky  legs.  The  hairy- veined  wings 
are  narrow,  somewhat  the  shape  of  mosquito  wings,  and  are  held 
erect  over  the  body  when  the  insect  is  in  repose.  The  wings  are 
quite  remarkable  for  the  inconspicuousness  of  the  crossveins  which 
gives  them  the  appearance  of  having  nine  or  ten  nearly  parallel 
longitudinal  veins.  The  antennae  are  long,  consisting  of  a  series 
of  beadlike  segments  with  whorls  of  hairs  at  the  joints.     The 


Fia.   212.      Life    history    of   phlebotomus   fly,    Phlebotomus   papatasii;     A,    egg; 
B,  larva;    C,  pupa;   D,  adult.     A,  X  80;    B,  C  and  D,  X  8.     (After  Newstead.) 

relatively  long  proboscis  is  made  up  in  practically  the  same  way 
as  is  that  of  a  mosquito  (see  p.  426),  except  that  the  needle-like 
organs  project  beyond  the  tip  of  the  sheath  made  for  them  by 
the  labium  or  lower  lip.  These  insects  are  usually  less  than 
one-fifth  of  an  inch  in  length  and  often  not  over  one-eighth  of 
an  inch ;  they  can  easily  crawl  through  the  meshes  of  an  ordinary 
mosquito  net,  and  are  therefore  hard  to  avoid.  Their  bites  are 
very  annoying  and  cause  an  amount  of  irritation  which  seems 
quite  out  of  proportion  to  the  size  of  the  insects.  In  most  cases 
it  is  only  the  female  which  sucks  blood,  but  in  some  species  the 


468 


OTHER  BLOOD-SUCKING  FLIES 


male  has  a  proboscis  equally  well  fitted  for  piercing  skin  and 
sucking  blood,  and  the  male  of  at  least  one  African  species  is 
known  to  bite  as  well  as  the  female.  Most  if  not  all  of  the  spe- 
cies are  nocturnal  or  become  active  at  twilight  only.  In  Corsica, 
for  instance,  it  is  said  to  be  very  difficult  to  capture  these  midges 
except  for  about  one  hour  after  sunset.  During  the  daytime 
they  remain  hidden  away  in  dark  corners,  cellars,  crevices  of 
rocks,  etc. 

Life  History.  (Fig.  212.)  — ^  Most  species  of  Phlebotomus  lay 
their  eggs  in  crevices  of  rocks,  in  damp  cracks  in  shaded  soil,  on 

moist  rubbish,  in  crannies 
or  chinks  in  cement  of  dark 
cellars,  between  boards  in 
privies  and  cesspools,  and 
in  other  similar  situations. 
Most  species  seem  to  show 
a  decided  preference  for 
crevices  in  rocks,  and  find 
ideal  situations  in  ruins  of 
old  stone  buildings,  crum- 
bling rock  fences,  etc.  In 
Malta  Captain  Marett  found 
these  insects  breeding  only 
in  such  places.  In  Peru, 
according  to  Townsend,  the 
universal  type  of  fence,  a 
structure  of  rubble  and  loose 
rock,  provides  ideal  breed- 
ing places  for  the  species  found  there,  whereas  in  Italy  and 
Sicily  the  earthquake  ruins  furnish  equally  ideal  breeding  places 
for  them  (Fig.  213).  The  sandflies  which  occur  in  certain  parts 
of  Egypt  are  believed  to  breed  in  damp  cracks  in  the  sandy  soil, 
since  there  seem  to  be  no  other  suitable  places. 

The  eggs  are  about  40  to  50  in  number  and  are  usually  all  laid 
at  approximately  one  time,  being  literally  shot  out  by  the  female 
to  a  distance  several  times  the  length  of  the  abdomen.  The 
eggs  are  viscid  and  adhere  to  the  surfaces  with  which  they  come 
in  contact;  it  would  seem  that  the  peculiar  method  of  ejecting  the 
eggs  is  a  protective  adaptation,  facilitating  their  deposition  in 
the  farthest  reach  of  a  crevice  where  even  the  tiny  insect  itself 


Fig.  213.  An  earthquake  ruin  in  Sicily, 
affording  favorite  breeding  places  for  phle- 
botomus flies. 


LIFE  HISTORY  OF  PHLEBOTOMUS  FLIES 


469 


could  not  penetrate.  The  eggs  are  elongate  and  are  of  a  dark, 
shiny  brown  color,  with  fine  surface  markings  which  vary  in 
different  species  (Fig.  214). 

The  incubation  in  the  case  of  the  common  Old  World  P. 
papatasil  requires  from  six  to  nine  days  under  favorable  con- 
ditions, but  the  eggs  are  very  susceptible  to 
external  conditions,  and  die  quickly  if  ex- 
posed to  sunlight  or  if  not  kept  damp.  The 
larvae  (Fig.  212B)  are  tiny  caterpillar-like 
creatures  with  a  relatively  large  head  with 
heavy  jaws  (Fig.  215),  and  with  two  pairs 
of  bristles  on  the  last  segment  of  the  abdo- 
men, one  pair  of  which  are  sometimes  nearly 
as  long  as  the  body  and  are  held  erect  and 
spread  out  fanlike;  in  the  newly  hatched  fig.  214. 
larvae  there  is  only  one  pair  of  bristles.     The  phiebotomus  flies;  A,  P. 

.       ,        .  •  1     1         -,1  i       ii       1    papatasii;  B,  P.   argen- 

body  is  provided  with  numerous  toothed  np^s;  c,  P.  minutus. 
spines  which  give  it  a  rough  appearance,  x  about  200.  (After 
These  spines  have  recently  been  shown  by  ^'^^  • 
Howlett  to  differ  in  different  species  and,  together  with  the  rela- 
tive length  of  the  caudal  bristles,  to  form  good  identification 
marks.  The  whole  length  of  the  larva  of  P.  papatasii  when 
full  grown  is  less  than  one-fifth  of  an  inch,  and  is  therefore  not  so 
large  as  an  ordinary  rice  grain.  It  is 
quite  active  in  spite  of  the  fact  that  it 
has  neither  legs  nor  eyes;  it  progresses 
in  the  manner  of  a  caterpillar,  holding 
to  a  rock  or  board  with  the  tip  of  the 
abdomen  while  stretching  the  body,  then 
hiding  with  the  doubled-under  head  while 
drawing  up  the  body  again.  It  feeds  on 
decaying  vegetable  matter,  and  probably 
also  on  moulds,  etc.  When  exposed  to 
light  the  larva  of  P.  papatasii  has  the 
pecuUar  habit  of  flicking  itself  off  the  surface  on  which  it  has 
been  resting.  On  approach  of  danger,  Phiebotomus  larvae  often 
"  play  'possum  "  and  feign  death. 

The  full  development  of  the  larvae  requires  from  three  weeks 
to  two  months  or  more,  depending  almost  entirely  on  the  tem- 
perature.    Larvae  which  hatch  at  the  beginning  of  cold  weather 


Fig.  215.  Front  view  of 
head  of  Phiebotomus  minu- 
tus larva.  Much  enlarged. 
(After  Howlett.) 


470  OTHER  BLOOD-SUCKING  FLIES 

do  not  pupate  until  the  following  spring.  When,  after  several 
moults,  they  go  into  the  resting  pupal  stage  the  last  larval  skin 
with  its  caudal  bristles  remains  adhering  to  the  posterior  end. 
The  pupa  (Fig.  212C)  is  characterized  by  a  very  rough  cuticle 
over  the  thorax,  but  can  be  identified  best  by  the  adhering  larval 
skin.  It  is  colored  so  much  like  its  surroundings,  and  looks  so 
much  like  a  tiny  bit  of  amorphous  matter,  that  it  is  very  difficult 
to  find.  In  warm  weather  the  adult  insect  emerges  after  from 
six  to  ten  days,  but  this  is  much  prolonged  by  low  temperatures. 
The  entire  life  cycle  from  the  laying  of  the  eggs  to  the  emergence 
of  the  adults  may  be  passed  through  in  a  month  in  hot  weather, 
according  to  Howlett's  observations  on  an  Indian  species,  though 
it  takes  two  months  or  more  in  cool  weather.  In  Malta,  accord- 
ing to  Newstead,  the  cycle  takes  about  three  months. 

Phlebotomus  and  Disease.  Phlebotomus  Fever.  —  Although 
sandflies  have  been  accused  of  transmitting  a  number  of  human 
diseases  in  various  parts  of  the  world,  in  most  cases  their  actual 
role  has  not  been  determined  beyond  doubt.  The  most  im- 
portant relation  of  sandflies  to  disease  is  in  connection  with  a 
relatively  mild  febrile  disease  sometimes  known  as  three-days, 
fever,  but  more  commonly  known  as  phlebotomus  fever  or 
papataci  fever  from  the  name  of  the  transmitter,  Phlebotomus 
papatasii.  The  nature  of  the  disease  and  the  role  of  the  sandfly 
in  carrying  it  is  discussed  in  Chap.  X,  p.  188.  As  in  the  case 
of  many  other  insect-borne  diseases,  the  relation  of  the  insects 
to  the  disease  was  suspected  for  a  long  time  before  the  scientific 
proof  of  it  was  made.  It  was  not  until  1908  that  Doerr  demon- 
strated the  part  played  by  sandflies. 

The  principal  species  concerned  in  the  transmission  of  phle- 
botomus fever  is  P.  papatasii,  but  it  is  possible  that  other  species, 
especially  P.  perniciosus  and  P.  minutus,  both  of  Mediterranean 
countries,  may  also  be  involved,  though  as  far  as  is  known  the 
disease  does  not  occur  outside  the  range  of  the  first-named  species 
except  at  Aden. 

P.  papatasii  (Fig.  212D)  is  of  medium  size,  reaching  about  one- 
eighth  of  an  inch  in  length,  pale  yellowish  gray  in  color  with 
a  dull  red-brown  stripe  down  the  middle  of  the  thorax  and  a  spot 
of  the  same  color  at  either  side.  It  is  found  in  many  parts  of 
southern  Europe,  North  Africa  and  in  southern  Asia.  It  has 
the  typical  habits  of  the  genus,  preferring  to  lay  its  eggs  in 


PHLEBOTOMUS   FLIES  AS   DISEASE  CARRIERS  471 

crevices  in  damp  cellars,  in  caves,  cracks  in  broken  walls,  etc.  In 
Malta  the  life  cycle  of  this  species  has  been  observed  to  take  about 
three  months,  but  under  ideal  conditions  it  would  probably  be 
shorter. 

The  adult  fly,  as  observed  in  Malta,  where  it  has  been  most 
extensively  studied,  chooses  caves,  catacombs  and  other  similar 
places  as  its  favorite  localities.  On  still,  warm  nights  it  is  com- 
mon in  houses,  but  rarely  appears  when  there  is  a  cool  fresh  breeze. 
Some  houses  were  found  to  be  much  more  infested  than  others, 
possibly  due  to  the  proximity  of  suitable  breeding  places  and  to 
the  lack  of  breezes.  Newstead  found  that  dark  rooms  on  the 
sheltered  side  of  the  first  floor  of  a  house  were  most  likely  to  be 
infested;  only  one  individual  was  found  on  the  second  floor. 
The  distance  which  the  adults  travel  is  thought  to  be  very  short, 
but  they  may  be  carried  by  public  conveyances,  and  infection 
has  been  known  to  be  transplanted  long  distances  by  flies  carried 
on  coasting  vessels. 

Phlebotomus  and  Other  Diseases.  —  Sandflies  have  frequently 
been  suspected  of  complicity  in  the  spread  of  the  parasites  of 
oriental  sore,  though  no  definite  proof  of  this  has  ever  been 
brought  out.  Wenyon,  from  his  study  of  oriental  sore  at  Bag- 
dad, believed  that  these  flies,  as  well  as  certain  other  insects, 
might  easily  be  concerned  in  the  spread  of  the  infection,  but  he 
did  not  have  an  opportunity  to  test  his  belief.  Recently  a 
number  of  French  workers  in  North  Africa,  including  Laveran 
and  the  Sergents,  have  advanced  the  theory  that  P.  minutus 
var.  africanus  is  the  carrier  of  the  infection,  and  that  certain 
lizards  or  geckos  of  the  region,  Tarentola  mauritanica,  serve  as  a 
reservoir  for  the  disease.  Parasites,  closely  resembling  Leish- 
man  bodies  which  cause  oriental  sore,  have  been  found  in  the 
blood  of  geckos  taken  near  Tunis,  and  it  is  well  known  that  rep- 
tiles are  an  important  if  not  the  prime  source  of  food  for  the 
various  species  of  Phlebotomus,  and  P.  minutus  especially  harasses 
the  North  African  gecko.  Roubaud  found  a  lizard  in  West 
Africa  which  was  covered  with  gorged  females  of  this  species 
and  in  India  P.  minutus  is  said  to  prefer  geckos  to  man  as  a 
source  of  food.  It  is  interesting  to  note  in  this  connection  that 
the  forest  workers  in  Paraguay,  where  the  more  serious  American 
type  of  leishmaniasis  is  found,  believe  the  infection  to  be  caused 
by  the  bite  of  blood-sucking  arthropods  which  have  fed  on  snakes. 


472  OTHER  BLOOD-SUCKING  FLIES 

Phlehotomus  minutus  is  a  buff-colored  sandfly.  It  is  small,  even 
for  a  Phlehotomus;  the  female  measures  only  about  yV  of  an  inch 
in  length  and  the  male  considerably  less  than  this. 

Other  diseases  with  which  Phlehotomus  has  been  connected 
are  two  which  occur  together  in  certain  regions  of  the  Peruvian 
Andes,  namely,  Oroya  fever  and  verruga  peruviana  (see  Chap. 
X,  p.  178).  These  diseases,  as  pointed  out  elsewhere,  have 
long  been  confused,  and  even  yet  are  held  by  some  investigators 
to  be  different  phases  of  the  same  disease.  Townsend,  of  the 
U.  S.  Department  of  Agriculture,  spent  two  years  in  Peru  in- 
vestigating the  diseases  (which  he  considers  identical)  and  came 
to  the  conclusion  that  Phlehotomus  verrucarum  is  the  transmitter, 
basing  his  conclusions  on  the  distribution  and  habits  of  the  in- 
sect, and  on  certain  experiments  which  he  undertook.  The  sand- 
fly in  question,  which  was  discovered  and  named  by  Townsend, 
is  the  only  nocturnal  insect  which  is  closely  limited  in  its  dis- 
tribution to  approximately  the  same  localities  as  is  Oroya  fever 
and  verruga,  and  it  seems  to  be  well  established  that  the  disease 
is  contracted  at  night.  Townsend  believes  that  he  obtained  proof 
of  the  transmission  of  verruga,  and  obtained  a  typical  breaking 
out,  by  injecting  into  a  dog  the  macerated  bodies  of  insects  which 
had  fed  on  a  verruga  patient,  but  his  results  have  not  been  widely 
accepted.  If,  as  is  now  more  generally  believed,  Oroya  fever  and 
verruga  are  really  distinct,  then  it  is  possible  that  P.  verrucarum 
may  be  the  carrier  of  both  diseases,  or  of  either  one  or  the  other. 
If  this  insect  acts  as  a  carrier  for  both  diseases,  which  would  be 
a  very  unusual  situation,  this  fact  would  explain  the  close  limi- 
tation of  the  two  diseases  to  nearly  the  same  zones,  and  would 
also  explain  the  frequency  with  which  the  two  infections  occur 
simultaneously  or  following  each  other.  That  oroya  fever  is  an 
insect-borne  disease  is  almost  certain,  and  it  is  quite  likely  that 
the  sandfly  discovered  by  Townsend  will  be  found  to  be  the 
carrier  of  it.  Verruga,  however,  is  a  smallpox-like  disease  and 
may  be  contagious  rather  than  infective. 

Phlehotomus  verrucarum  is  a  species  of  sandfly  which  breeds 
principally  in  the  damp  recesses  of  the  loose  rubble  fences  which 
are  so  universally  used  in  Peru,  and  probably  feeds  largely  on  a 
species  of  lizard,  Tropidurus  peruviamis,  which  inhabits  the  same 
rock  fences.  According  to  Townsend  it  requires  for  its  life  cycle 
a  fairly  high  total  of  summer  heat  and  much  moisture,  with  an 


TRUE  MIDGES   (CHIRONOMID^)  473 

absence  of  night  fogs  and  of  low  winter  temperatures.  The 
adults  will  not  live  where  there  are  continuous  strong  air  currents. 
These  conditions  limit  the  species  closely  to  the  deep-cut  canyons 
or  ''  quebradas  "  (Fig.  53),  between  3000  and  8000  ft.  elevation,  on 
the  west  face  of  the  Andes.  There  is  certainly  a  remarkable 
agreement  between  this  distribution  and  that  of  Oroya  fever. 

Control.  —  Sandflies  are  very  difficult  insects  to  deal  with,  both 
on  account  of  the  small  size  of  the  adults  and  of  the  nature  of 
the  breeding  places. 

The  only  precaution  that  can  be  employed  to  keep  the  adults 
out  of  houses  during  warm  weather  is  the  use  of  repellents. 
Spraying  mosquito  netting  with  some  repelling  substance,  such  as 
odorous  oils,  e.g.,  anise  oil,  eucalyptus  oil,  etc.,  or  with  a  weak 
solution  of  formalin,  or,  in  fact,  with  any  of  the  repelling  sub- 
stances mentioned  in  connection  with  mosquitoes,  serves  to  keep 
the  insects  out  as  long  as  the  odor  lasts.  The  insects  are  attracted 
toward  a  light,  and  are  therefore  usually  very  abundant  in  lighted 
rooms  on  warm  still  nights.  A  gentle  breeze  or  a  current  of  air 
from  electric  fans  placed  near  the  windows  prevents  their  entrance 
and,  as  has  already  been  mentioned,  upstairs  rooms  are  practi- 
cally immune.  Personal  protection  can  be  obtained  by  appli- 
cations of  repellents.  Townsend  recommends  equal  parts  anise 
oil,  eucalyptus  oil  and  oil  of  turpentine  in  a  boric  acid  ointment. 

It  is  almost  impossible  to  destroy  sandflies  in  their  early  stages. 
Townsend  thinks  that  the  elimination  of  rubble  fences  in  Peru 
would  reduce  their  numbers,  at  least  locally,  but  it  would  be 
far  from  a  simple  problem  to  destroy  all  possible  breeding  places, 
even  within  a  very  small  radius.  In  Europe,  where  stone  and 
cement  are  more  extensively  used  than  in  America,  the  problem 
is  still  greater.  The  earthquake  ruins  of  Sicily,  as  has  been 
mentioned  before,  give  unlimited  breeding  places.  The  large 
numbers  of  these  insects  in  parts  of  Egypt  where  such  places  are 
not  available  indicate  that  damp  cracks  in  soil  may  be  utilized 
as  breeding  places,  and  it  would  be  obviously  impossible  to 
eliminate  these  or  to  treat  them  thoroughly. 

True  Midges  (Chironomidae) 

General  Account.  —  The  family  Chironomidae  comprises  a 
large  number  of  species  of  small  flies,  sometimes  almost  micro- 
scopic, found  all  over  the  world.     The  larger  ones  quite  closely 


474  OTHER  BLOOD-SUCKING  FLIES 

resemble  mosquitoes  except  for  the  absence  of  the  long  proboscis, 
and  the  dancing  flocks  of  these  insects  which  can  be  seen  over 
pools  or  swamps  on  any  summer  day  are  usually  taken  for  mos- 
quitoes without  question.  As  expressed  by  Riley  and  Johann- 
sen,  ''  these  midges,  especially  in  spring  or  autumn,  are  often  seen 
in  immense  swarms  arising  like  smoke  over  swamps,  and  pro- 
ducing a  humming  noise  which  can  be  heard  for  a  considerable 
distance."  In  such  swamps  the  larvae,  most  of  which  are  aquatic 
and  live  in  the  mud  or  amid  aquatic  vegetation,  may  be  scooped 
up,  literally  by  the  shovelful.  Fortunately  the  great  majority 
of  these  insects  are  quite  harmless,  in  fact,  inasmuch  as  the 
larvae  are  an  important  food  for  young  fishes,  they  are  distinctly 
beneficial.     The  blood-sucking  species  belong  to  the  subfamily 


D 


Fig.  216.  Life  history  of  blood-sucking  midge,  CuHcoides;  A,  adult  male  (C 
reticulatus) ,  X  5;  B,  eggs  (C.  marium),  X  18;  C,  larva  (C.  reticulatus) ,  X  5;  D, 
pupa  (C  marium),   X  10.     (After  Lutz.) 

Ceratopogoninse  and  are  very  small;  only  the  females  are  known 
to  suck  blood.  They  are  well  known  to  hunters  and  anglers  and 
other  frequenters  of  the  woods  in  most  parts  of  the  world.  In 
America  they  are  usually  called  "  gnats  "  or  ''  punkies  "  and  in 
the  West  are  known  as  "  no-see-ums,"  on  account  of  their  very 
small  size. 

These  insects  (Fig.  216)  can  usually  be  distinguished  from 
allied  insects  by  the  peculiar  venation  of  the  wings,  the  first  two 
veins  being  very  heavy  while  the  others  are  indistinct.  Though 
the  bodies,  and  sometimes  to  a  slight  degree  the  wings,  are  more 
or  less  hairy  the  scales  so  characteristic  of  mosquitoes  are  ab- 
sent. The  proboscis  is  never  long  even  in  the  blood-suckers, 
and  one  is  led  to  marvel  at  the  irritation  which  can  be  inflicted 
by  such  a  small  insect  with  such  a  small  organ.     Usually  midges 


LIFE  HISTORY  OF  CHIRONOMIDS  475 

rest  with  the  front  legs  elevated,  though  not  all  species  have  this 
habit.  In  most  Chironomidae  the  thorax  of  the  adult  insect 
projects  like  a  hood  over  the  head,  but  in  the  subfamily  Cera- 
topogoninse,  which  alone  interests  us  here,  this  is  not  the  case, 
and  this  negative  characteristic  is  the  best  distinguishing  mark 
of  the  subfamily. 

There  are  a  number  of  genera  and  many  species  included  in 
this  group  of  blood-suckers,  but  they  fall  naturally  into  two  groups 
according  to  the  habits  and  structure  of  the  larvae.  In  one,  of 
which  the  principal  genera  are  Ceratopogon  and  Forcipomyia, 
the  larvae  differ  from  all  other  Chironomidae  in  being  terrestrial, 
living  in  damp  places  under  bark,  stones,  moss,  etc.,  and  in  being 
covered  with  spines  (Fig.  217).  In  the  other  group,  of  which  the 
principal  genus  is  Culi- 
coides,  the  larvae  are 
orthodox  in  being 
aquatic  and  unspined 
(Fig.  216C);  a  few  spe-       ^'°-  ^i^-  ^^^^^  o^F^^.Ap^viasr.c.larU. 

cies  are  marine.      Most 

of  the  blood-sucking  midges  become  active  at  dusk,  but  if  dis- 
turbed they  will  bite  in  the  shade  even  on  bright  sunny  days. 

Life  History.  —  The  eggs  of  aquatic  midges  (Fig.  216B),  sev- 
eral hundred  in  number,  are  laid  in  water,  either  floating  free  or 
moored  to  some  object.  Each  one  is  covered  with  a  gelatinous 
envelope,  and  the  eggs  adhere  in  chains  or  in  little  masses,  thus 
resembling  very  diminutive  bunches  of  frog  or  toad  eggs.  In 
about  six  days,  more  in  case  of  low  temperature,  the  eggs  hatch 
into  almost  microscopic  larvae  (Fig.  216C).  The  latter  are  worm- 
Hke  creatures  practically  without  hairs  or  spines  in  the  aquatic 
species,  but  with  conspicuous  bristles  in  the  terrestrial  forms. 
Usually  the  only  hairs  present  are  in  a  pair  of  tufts  on  the  last 
segment.  In  most  midge  larvae  there  is  a  footlike  outgrowth 
on  the  first  and  last  segments  of  the  abdomen.  The  larvae  have 
inconspicuous  blood-gills  for  breathing  in  water,  and  therefore 
do  not  need  air  as  do  mosquito  larvae.  Most  midge  larvae  are 
free-swimming,  but  some  excavate  tubes  in  mud  and  line  them 
with  a  salivary  secretion  which  hardens  on  contact  with  water. 
The  food  consists  of  microscopic  plant  and  animal  life.  The 
pupa  (Fig.  216D)  rather  resembles  that  of  a  mosquito,  except 
that  the  abdomen  is  kept  extended  instead  of  curled  under  and 


476  OTHER  BLOOD-SUCKING  FLIES 

the  pupa  floats  in  a  vertical  position,  breathing  through  tufts  of 
threadUke  filaments  which  correspond  to  the  breathing  trumpets 
of  mosquitoes.  In  the  terrestrial  forms  the  pupa  retains  the 
last  larval  skin  hanging  to  its  posterior  end.  The  aquatic  species 
of  the  subfamily  Ceratopogoninae  are  peculiar  in  that  the  pupa) 
must  reach  a  dry  surface  before  the  adult  will  emerge.  Little 
is  known  about  the  length  of  time  required  for  the  development 
from  egg  to  adult,  but  it  is  probably  comparable  with  that  re- 
quired by  mosquitoes  —  two  weeks  or  less  to  a  month  or  more, 
according  to  temperature. 

Annoyance.  —  The  amount  of  annoyance  which  may  be  caused 
by  midges  is  sometimes  very  great.  The  writer  will  never  for- 
get his  experiences  with  them  in  a 
collecting  and  fishing  trip  in  the 
Cascade  Mountains  of  Oregon. 
The  midge  which  proved  itself 
troublesome,  a  species  of  Culicoides 
(Fig.  218),  was  very  local  in  dis- 
tribution, and  always  standing 
pools  of  shallow  water  were  found 
in  the  near  vicinity.  The  prox- 
imity of  such  pools  was  invariably 
Fig.  218.  A  "punky"  or  "no-  proclaimed,  towards  evening,  by 
see-nmr   Culicoides,    which    is   a  ^^^  collection  of  great  numbers  of 

scourge  of  fishermen  and  campers  in  ° 

the  Cascade  Mountains  of  Oregon,    these   insects    On  all   expOSed    parts 

^  ^^-  of  the  body,  each  one  so  minute  as 

to  be  hardly  visible,  but  in  the  aggregate  sometimes  giving  the 
arm  or  shirt  sleeve  a  dark  gray  color.  Each  one  is  presently 
the  cause  of  an  intensely  itching  spot.  That  the  insects  are 
attracted  by  animal  smells  is  evident  from  the  following  experi- 
ence. The  writer  had  shot  a  rabbit  and  was  skinning  it.  Al- 
most immediately  after  the  animal  was  cut  open  and  the  smell 
of  the  warm  bowels  exposed  to  the  air  the  writer  found  himself 
attacked  by  myriads  of  these  insects,  and  was  bitten  to  such 
an  extent  as  to  be  driven  almost  to  a  complete  frenzy,  until  he 
discovered  that  only  a  few  yards  from  the  opened  animal  he  was 
not  attacked  at  all.  The  skinning  of  the  rabbit  was  completed 
in  the  welcome  protection  of  a  dense  smoke. 

Midges  as  Disease   Carriers.  —  Only  in  one  instance  have 
midges  been  accused  of  carrying  disease.     Two  species  of  land- 


CONTROL  OF  CHIRONOMIDS  477 

breeding  midges,  Forcipomyia  utce  and  F.  townsendi,  have  been 
incriminated  by  Townsend  as  the  carriers  and  intermediate  hosts 
of  the  protozoan  parasite  causing  "  uta  "  in  Peru.  Uta  (see 
Chap.  V,  p.  86)  is  a  form  of  leishmaniasis  occurring  on  the 
western  face  of  the  Andes.  According  to  Townsend,  Leishman 
bodies  are  found  in  abundance  in  the  digestive  tract  of  these 
midges,  and  injection  into  laboratory  animals  of  serum  contain- 
ing the  ground  bodies  of  captured  insects  resulted  in  the  forma- 
tion of  sores  which  Townsend  regarded  as  uta,  and  from  which 
he  obtained  a  few  Leishman  bodies.  Two  cases  are  cited,  also,  in 
which  uta  sores  developed  following  the  bites  of  the  midges,  and 
supposedly  due  to  them.  According  to  Townsend  the  infection 
is  evidently  transmitted  by  contamination  of  the  wound  made  by 
the  proboscis  with  infected  excrement.  That  these  insects  are 
really  the  transmitters  of  uta  in  man  cannot  be  considered  as 
proved,  but  it  must  be  regarded  as  a  possibility.  It  should  be 
recalled  that  many  insects  have  been  accused  of  carrying  Oriental 
sore  and  allied  diseases,  among  which  are  blackflies  (Simulium) , 
sandflies  (Phlehotomus) ,  gadflies  (Tabanidse)  and  others,  and  it 
is  open  to  question  whether  any  insect  which  harbors  a  Her- 
petomonas  in  its  gut  may  not  be  able  to  infect  vertebrates  if  the 
germs  reach  the  blood.  If  so,  these  midges  must  be  regarded  as 
conveyors  of  a  Leishmania  infection. 

Little  is  known  about  these  species  of  Forcipomyia,  but  it  is 
probable  that  their  habits  are  similar  to  those  of  better  known 
species.  In  the  North  American  species,  the  larvae  (Fig.  217) 
are  slender  whitish  worms  about  one-eighth  of  an  inch  in  length 
which  live  in  damp  places  in  moss  and  under  bark,  stones,  etc. 
The  pupae  are  pale  yellowish,  later  becoming  brown. 

Control.  —  The  control  of  the  aquatic  biting  midges  is  not 
difficult,  and  can  be  accomplished  in  the  same  manner  as  can  the 
control  of  swamp-breeding  mosquitoes,  by  draining,  stocking  with 
natural  enemies  or  oiling.  It  is  improbable  that  these  midges 
breed  to  any  extent  in  transient  pools,  for  most  of  them,  at  least, 
prefer  pools  of  standing  water,  abundant  in  organic  debris  and 
microscopic  organisms.  The  terrestrial-breeding  forms  of  For- 
cipomyia and  Ceratopogon,  like  the  sandflies,  are  practically  im- 
possible to  exterminate. 

Much  protection  from  the  adults  can  be  obtained  by  the  use 
of  repellents  as  advised  for  mosquitoes  and  sandflies  (see  p.  455). 


478 


OTHER  BLOOD-SUCKING  FLIES 


Blackflies  or  Buffalo  Gnats 


Fig.  219.     Blackfly,  Simulium 
pecuarum.    X  7.    (After  Riley.) 


General  Account.  —  The  blackflies,  as  annoy ers  of  domestic 
animals  and  man,  are  among  the  most  important  of  insect  pests. 

The  females  are  most  insatiable  blood- 
suckers, and  have  been  known  to  at- 
tack cattle  in  such  swarms  as  to  kill 
them;  a  Himalayan  species,  accord- 
ing to  Alcock,  has  been  said  to  kill 
even  human  beings  in  the  same  way. 
These  small  insects,  which  constitute 
the  family  Simuliidae,  are  quite  unlike 
the  other  flies  of  the  group  to  which 
they  belong.  Instead  of  the  usual 
slender,  long-legged,  midgelike  flies  of 
this  group  we  have  in  the  blackflies 
small,  robust,  humpbacked  creatures 
with  short  legs  and  broad  wings,  rather 
resembling,  in  a  general  way,  minia- 
ture houseflies  (Fig.  219).  The  an- 
tennae are  composed  of  11  segments,  but  they  are  short  and 
stocky,  and  have  no  hairs  at  the 
joints.  The  proboscis  in  the 
female  is  short  but  heavy  and 
powerful,  while  in  the  male  it 
is  poorly  developed.  The  mouth- 
parts  are  made  up  of  the  same 
parts  as  in  mosquitoes,  but  are 
dagger-like  instead  of  needle- 
Hke  (see  Fig.  220).  Most  of  the 
northern  species  are  black  in 
color,   whence   their   name,   but      ^      «^„     ,,     ,  .  ,,    ,„ 

.     ,,                   .                 '         .  Fig.   220.     Mouthparts  of   blackfly, 

some     01     the     species     are     red-  SimuUum;  ant.,  antenna;  ep.,  epiphar- 

dish     brown     or     yellowish,     and  Y'\'^'  ^^P"  ^ypopharynx;  lab.,  labium; 

,                        .                •        1             •        1  label.,     labellum;      mand.,     mandible; 

they    may    be    variously    striped  max.,  maxilla;  max.  p.,  maxillary  pal- 

and    marked.      The    wings    are  p^^-    (After  Alcock.) 
either  clear  or  of  a  grayish  or   yellowish   color  with   the  few 
heavy    veins    near    the    anterior    margin    often     distinctively 
colored.     Some  of  the  species  are  not  over   one  mm.   {^  of 


--ant 


lofbcj. 


LIFE  HISTORY  OF  BLACKFLIES 


479 


an  inch)  in  length  and  the  largest  of  them  scarcely  exceed  one- 
fifth  of  an  inch. 

Life  History.  —  Unlike  the  mosquitoes  and  midges,  blackflies 
breed  in  running  water  and  few  streams  flow  too  swiftly  for 
them.  The  eggs  are  laid  in  large  masses,  up  to  many  thousands 
in  number,  by  a  number  of 
females.  The  eggs  (Fig.  221  A), 
which  are  elliptical  and  yellowish 
and  have  a  peculiar  slimy  coat- 
ing, are  deposited  by  some  spe- 
cies on  leaves  or  blades  of  grass 
which  are  occasionally  licked  by 
running  water,  the  weight  of 
the  eggs  sufficing  to  submerge 
them;  other  species  dart  into 
the  water  and  deposit  directly 
on  the  slimy  surfaces  of  sub- 
merged stones  or  twigs.  The 
author  found  a  favorite  breed- 
ing place  of  the  blackflies  in 
the  woods  of  Northern  Ontario 
(species  undetermined)  to  be  on 
the  slimy  boards  of  old  lumber 
chutes  over  which  water  was 
constantly  flowing.  It  requires 
at  least  a  week  for  the  eggs  to 
hatch. 

The  larva  (Fig.  221B)  as  soon 

as   hatched    attaches    itself   by   a  enlarged,    not    drawn   to    same    scale 

,  ,  1     i?  ii  3^^-  S-.  aiial  gills;  ant.,  antenna;  dev.  g. 

sucker  at  the  posterior  end  Ot  the  m.,  developing  gill   filaments  of  pupa; 

body    to    a    stone    or    other    sub-  S-  ^-^  gi^^  filaments;  m.  f.,  mouth  fans; 

.  p.  c,  wallpocket-like  pupal  case;   post. 

merged     object.        As     expressed  g.,  posterior  sucker.     (A,  after  Meczni^ 

by    Alcock,    "  one    of    the    most  ^^^    from     Jobbins-Pomeroy,     others 

,  ,      .   ,.        *  -  ,  • ,      1  e     .1  after  Jobbins-Pomeroy.) 

characteristic    attitudes    oi    the 

larva  is  to  sit  upright  on  the  end  of  its  tail,  —  to  use  the  lan- 
guage of  the  poets  of  the  daily  press,  —  with  its  mouth  fans 
standing  out  from  its  head  like  a  pair  of  shaggy  ears."  The 
"  mouth  fans,"  which  are  very  delicate  and  elegant,  are  used 
for  sweeping  microscopic  particles  into  the  mouth  as  they  are 
brought  by  the  running  water.     The  stump  of  a  leg  on  the 


Fig.  221.  Developmental  stages  of 
blackflies.  A,  egg  of  Simulium  venu- 
stum;  B,  larva  of  S.  hracteatum;  C,  pupa 
(in  pupal  case)  of  *S.  venustum;  all  much 


480 


OTHER  BLOOD-SUCKING  FLIES 


--prol. 


first  segment  (Fig.  222  prol.)  is  used  for  creeping,  in  conjunction 
with  the  posterior  sucker,  the  larva  looping  along  like  a  ''  meas- 
uring worm";  it  is  also  of  use  in  constructing  the  silken  cocoon 
from  the  secretions  of  the  salivary  glands.  This  single  little 
leg  has  a  crown  of  tiny  hooklets  which  make  it  possible  for  the 
possessor  to  hold  its  ground  even  in  a  torrent  of  water.     The 

salivary  glands  referred  to  are  quite 
unlike  those  of  other  insects,  in  that 
they  extend  clear  back  to  the  pos- 
terior end  of  the  body  (Fig.  222,  sal. 
gl.).  The  fluid  secreted  hardens  to 
silk  at  once  on  exposure  to  water, 
and  is  used  not  only  in  spinning  the 
cocoon,  but  also  in  spinning  anchoring 
threads  and  life-lines.  According  to 
Malloch,  the  larva  when  disturbed 
releases  its  hold  and  floats  downstream, 
holding  by  the  stumpy  leg  to  a  silken 
thread  which  is  being  spun  out,  and 
by  means  of  which  the  insect  later 
regains  its  former  position.  The 
larvae  breathe  by  means  of  tiny  gills 
which  can  be  projected  through  a  slit 
in  the  last  segment  of  the  abdomen 
(Figs.  221  and  222,  an.  g.).  The  larvae 
are  never  found  solitary,  as  would  be 


-sal-  gt. 


p-d19.tr. 


an.^7 


Fig.  222. 


— :post.d. 

Larva    of  black- 


fly,  Simuiium  venustum,  side  expected    from    the   manner   of  laying 
:rot°r'».T:  t^^^  eggs;  the  author  ha^  seen  the  boards 

dig.  tr.,  digestive  tract;   m.  f.,    on    the    bottom    of    a    log    chute    COm- 

reklr  td  Toksr tst't  Pletely  covered  with  mosshke  patches 

posterior  sucker;  sal.  gl.,  saii-  of  these  larvae  for  areas  of  a  square 

vary  and  spinning  gland.  ^^^^  ^^  ^^^^ 

After  four  or  five  weeks,  in  summer,  the  larvae  prepare  to  go 
into  the  resting  pupal  stage,  and  spin  for  themselves  a  partial 
cocoon  which  is  variously  shaped  like  a  jelly  glass,  slipper,  wall 
pocket,  etc.,  open  at  the  upper  end  for  the  extrusion  of  the 
branching  gill  filaments  which  are  used  as  breathing  organs  (Fig. 
22 IC).  Some  species,  simply  spin  a  snarl  of  threads,  the  work 
of  a  whole  community,  in  the  meshes  of  which  the  pupae  exist  in 
a  fair  state  of  protection.     The  general  form  of  the  pupae  can  be 


BLACKFLIES 


481 


seen  in  Fig.  223.     The  breathing  filaments  vary  greatly  in  dif- 
ferent species  and  may  have  from  four  to  60  branches. 

The  adults  escape  from  the  pupae  after  from  one  to  three 
weeks  through  a  slit  in  the  back,  and  are  carried  safely  to  the 
surface  by  a  bubble  of  air  which  has  been  collecting  inside  the 
old  pupal  skin.  The  adults  are  short  lived  and  lay  their  eggs 
soon  after  emergence.  The  whole  life  of  a  gen- 
eration from  egg  to  egg  may  be  passed  in  from 
six  weeks  to  two  months  or  more.  Some  spe- 
cies have  several  generations  a  year  but  the 
majority  produce  but  a  single  brood  a  year. 
The  Canadian  species  already  referred  to  is 
seen  only  for  a  few  weeks  in  May  and  early 
June,  during  which  time  it  is  locally  exces- 
sively abundant.  Most  species  are  diurnal, 
but  the  author  found  the  Ontario  species  to 
be  most  active  from  late  afternoon  until  dark, 
and  again  early  in  the  morning.  This  species 
will  also  bite  readily  at  night  in  the  presence  of 
artificial  light. 

The  species  of  blackfiies  are  numerous,  but 
are  all  included  in  the  single  genus  Simulium, 
with  several  subgenera  which  some  workers 
elevate  to  the  rank  of  true  genera.  Some 
species  do  not  attack  man  but  viciously  attack 
various  domestic  animals.  While  on  a  collect- 
ing trip  in  the  Cascade  Mountains  of  Oregon  (After  Jobbins-Pom- 
the  author  found  it  necessary  to  keep  the  pack 
animal  picketed  in  the  smoke  of  the  camp  fire  constantly  to  pro- 
tect the  poor  creature  from  the  blackfiies  which  congregated  in 
large  numbers  about  his  eyes  and  nose,  yet  neither  the  author  nor 
his  companion  was  ever  bitten  by  one  of  these  flies.  One  of  the 
most  troublesome  species  in  the  United  States  is  *S.  pecuarum, 
the  famous  buffalo  gnat  of  the  south  central  portion  of  the  country. 
This  species  was  formerly  more  abundant  than  now,  and  was  a 
terrible  scourge  to  mules  and  cattle.  S.  venustum  is  one  of  the 
most  important  molesters  of  man.  It  occurs  over  the  greater 
part  of  the  eastern  portion  of  North  America. 

Annoyance.  —  In   the    estimation    of   the   author,    no   insect 
scourge  he  has  ever  experienced  is  more  terrible  than  an  attack 


Fig.  223.  Pupa 
of  blackfly,  Simu- 
lium jenningsi,  re- 
moved from  case; 
e.,  eye;  I.e.,  leg 
cases;  br.  f.,  breath- 
ing filaments  or  gills; 
w.     c,     wing     case. 


482  OTHER  BLOOD-SUCKING  FLIES 

of  blackflies  as  he  encountered  them  in  Canada.  From  ac- 
counts of  other  authors  they  must  be  equally  terrible  in  other 
places.  King,  for  instance,  states  that  in  parts  of  Sudan  (Don- 
gola)  a  species  known  as  the  nimetti,  Simulium  griseicollis, 
renders  life  a  burden  during  the  winter  months.  The  famous 
Columbacz  fly,  S.  columhaczense,  of  southern  Europe  is  said  to 
be  a  terrible  pest,  and  there  are  instances  of  children  having  been 
killed  by  it.  My  own  experiences  occurred  in  the  woods  of 
Northern  Ontario  early  in  June.  Upon  arriving  there  I  did  not 
recognize  Dr.  Munford  of  Cornell  University,  with  whom  I 
had  been  quite  intimate,  until  he  spoke.  He  had  been  in  the 
region  about  a  fortnight.  His  face,  neck  and  arms  were  so  swol- 
len from  blackfly  bites  as  to  completely  alter  his  appearance. 
The  wrists  were  swollen  until  no  constriction  between  hand  and 
forearm  was  present.  That  evening,  having  been  told  of  the 
manner  in  which  deer  came  and  stood  in  the  water  near  the 
outlet  of  the  lake,  a  mile  or  so  from  camp,  I  went  in  a  canoe  to 
watch  them,  being  warned  to  tie  my  trouser  legs  tightly  around 
my  shoes  and  my  coat  sleeves  to  my  gloves,  and  to  fit  a  veil 
stretched  from  a  broad-brimmed  hat  tightly  around  my  neck. 
No  repellents  were  at  hand.  With  some  impatience  (having  been 
bred  among  the  mosquitoes  of  New  Jersey)  I  submitted  to  these 
precautions,  though  I  was  careless  in  carrying  them  out,  and 
made  the  trip  to  the  outlet  which  is  an  old  log  chute,  and  the 
breeding  place  of  the  flies.  In  spite  of  the  precautions  taken, 
the  blackflies,  alighting  on  the  veil  in  such  numbers  as  to  make 
it  difficult  to  see  through  it,  managed  to  find  vulnerable  spots 
in  my  armor.  Unlike  mosquitoes  they  alight  and  crawl;  they 
found  their  way  up  under  the  veil,  between  the  buttons  of  shirt 
and  trousers,  and  through  the  cords  at  my  wrists.  In  a  few 
minutes  I  was  driven  almost  frantic  and  could  hardly  restrain 
myself  from  diving  into  the  lake  to  avoid  the  attacking  flies,  as 
did  the  deer.  Each  bite,  and  before  I  got  to  the  safe  haven  of  a 
dense  smudge  at  camp  I  had  hundreds  of  them,  was  only  slightly 
painful;  the  flies  drilled  a  tiny  hole  which  bled  a  drop  or  two,  so 
that  the  attacked  parts  of  the  body  became  completely  smeared 
with  blood.  But  this  was  not  the  end.  The  bites  next  morning 
were  swollen,  and  itched  somewhat;  the  swelling  and  irritation 
grew  constantly  worse  until  the  third  night,  when  each  bite 
became  the  site  of  an  oozing  pimple.     By  this  time  the  itching 


CONTROL  OF  BLACKFLIES  483 

was  so  intense  that  I  was  in  agony  all  night  and  could  not  sleep. 
Accompanying  this  there  was  a  feeling  of  general  ''  ennui " 
and  despondence  with  some  fever,  due,  no  doubt,  to  the  action 
of  the  poison  injected  by  the  numerous  insects.  Subsequent 
attacks  by  the  flies,  though  always  far  from  pleasant,  were  not 
so  severe  in  their  effects,  a  certain  amount  of  immunity  appar- 
ently having  been  built  up.  On  account  of  the  slow  develop- 
ment of  the  symptoms  it  was  my  belief  that  possibly  they  were 
due  to  the  injection  of  a  living  organism.  Stokes,  however, 
has  shown  that  the  effects  of  blackfly  bites,  essentially  as  de- 
scribed above,  can  be  reproduced  by  the  injection  of  material 
from  preserved  flies.  An  interesting  suggestion  is  made  by 
Stokes  that  possibly  the  first  bites  of  the  flies  sensitize  the  body 
to  the  particular  poison  injected  so  that  it  reacts  rather  violently 
to  subsequent  injections  of  it.  This  phenomenon,  which  is 
known  to  occur  in  connection  with  many  poisonous  substances, 
is  a  form  of  anaphylaxis  (see  p.  24).  Possibly  the  rashes  pro- 
duced by  mites,  lice,  etc.,  may  also  be  due  to  such  a  reaction. 

As  yet  blackflies  are  not  known  to  be  the  carriers  of  any  dis- 
eases. A  theory  was  rampant  a  few  years  ago  that  pellagra  was 
due  to  a  protozoan  transmitted  by  blackflies,  but  it  is  now  gen- 
erally held  that  this  disease  is  due  to  an  imperfect  diet,  or  rather 
to  lack  of  the  necessary  assortment  of  substances  in  the  diet, 
and  so  is  in  no  way  connected  with  blackflies  or  other  insects. 

Control.  —  Since  blackflies  breed  in  running  water  the  methods 
to  be  employed  in  their  extermination  are  quite  different  from 
those  ordinarily  used  in  the  extermination  of  mosquitoes.  One 
of  the  measures  most  widely  used  is  the  treatment  of  breeding 
streams  with  phinotas  oil,  a  poisonous  oil  which  forms  an  emul- 
sion in  the  water  and  slowly  soaks  through  it.  In  concentrations 
sufficient  to  destroy  the  larvae,  however,  this  oil  is  also  destruc- 
tive to  fish.  Often  the  breeding  grounds  of  blackflies  may  be 
locally  destroyed  or  reduced  by  damming  the  stream  at  inter- 
vals, leaving  falls  between,  or  in  the  case  of  small  brooks  by  the 
construction  of  underground  channels  or  of  a  drain-pipe  line. 
The  clearing  away  of  roots  and  fallen  logs  from  streams  is  often 
of  value,  in  that  it*  removes  surfaces  on  which  the  eggs  are  laid, 
and  obliterates  the  numerous  small  falls  which  are  ideal  for  the 
larvae.  In  larger  streams  the  cultivation  of  fishes,  such  as  trout, 
young  bass,  darters,  etc.,  greatly  reduces  the  number  of  black- 


484  OTHER  BLOOD-SUCKING  FLIES 

flies  if  it  does  not  eliminate  them  entirely.  In  such  cases  care 
should  be  taken  that  there  are  no  small  trickling  streams  which 
are  not  readily  reached  by  fish.  In  the  author's  experience 
streams  which  harbor  large  numbers  of  caddis  worms,  dragon-fly 
larvae  and  other  carnivorous  aquatic  insects  do  not  breed  black- 
flies  to  any  extent. 

A  considerable  degree  of  protection  from  blackflies  can  be 
obtained  by  the  use  of  repellents  such  as  are  used  for  mosquitoes, 
but  their  efficiency  seems  to  be  lost  more  quickly  than  in  the  case 
of  mosquitoes.  Moreover  the  crawling  habits  of  the  flies  must 
be  taken  into  account,  and  other  parts  of  the  body  than  those 
which  are  directly  exposed  must  be  treated.  Blackflies  may  be 
driven  from  houses  by  fumigation  with  pyrethrum  powder  or  by 
any  other  fumigation  method.  In  camp  life  the  use  of  smudges 
is  indispensable.  An  efficient  smudge  which  will  last  all  night 
can  be  made  in  an  old  bucket  with  a  few  holes  punched  near  the 
bottom.  A  small  fire  is  started  in  this  and  then  the  bucket  is 
filled  with  partly  wet,  punky,  decayed  wood  which  will  smoulder 
slowly  and  produce  a  dense  yellow  smoke.  Sleeping  in  the 
presence  of  such  a  smoke  is  at  first  almost  as  unpleasant  as  are 
attacks  by  mosquitoes  and  blackflies  (the  latter  becoming  active 
only  toward  dawn)  but  one  soon  becomes  accustomed  to  it, 
and  it  has  none  of  the  terrible  after-effects  of  an  attack  by  the 
flies. 

Gadflies  (Tabanidae) 

General  Account.  —  Although  primarily  of  importance  as 
blood-thirsty  pests  of  domestic  animals,  the  gadflies  or  horseflies 
(Tabanidae)  cannot  be  ignored  as  biters  of  human  beings,  es- 
pecially as  they  have  been  shown  to  be  implicated  in  the  spread 
of  certain  human  diseases.  The  bites  are  painful,  and  sometimes 
cause  annoyance  for  several  hours;  not  infrequently  these  bites, 
which  may  bleed,  subsequently  become  infected  and  give  rise 
to  troublesome  sores.  The  females  alone  are  bloodsuckers,  the 
males  living  chiefly  on  plant  juices.  These  flies,  of  which  over 
2500  species  have  been  recorded,  occur  in  every  part  of  the  world, 
and  in  every  sort  of  habitat  where  water  or  dahip  places  are  avail- 
able for  breeding  purposes. 

The  gadflies  are  of  large  size  and  heavy  build  (Fig.  224 A). 
They  are  often  beautifully  colored  in  black,  brown  and  orange 


TABANIDS 


485 


tones,  sometimes  with  brilliant  green  or  green-marked  eyes, 
though  in  most  species  of  temperate  climates  the  huge  eyes  are 
brown  or  black.  The  head  is  large,  and  in  the  male  is  almost 
entirely  occupied  by  the  eyes,  which  meet  across  the  crown  of 
the  head  (Fig.  224B),  though  in  the  females  a  narrow  space  is 


Fig.  224.  Life  history  of  a  Tabanid,  Tabanus  kingi,  a  "seroot"  of  Sudan.  A, 
adult  female,  XS;  B,  head  of  adult  male,  X  3;  C,  egg  mass,  laid  in  crevices  of  rock, 
X  5;   Z),  larva,    X  2^;   E,  pupa,    X  2|.     (After  King.) 


left  between  them.  The  antennae  are  of  characteristic  shape 
(Fig.  21 IC)  varying  somewhat  in  the  different  genera.  The 
mouthparts  (Fig.  225)  are  almost  exactly  Uke  those  of  the 
blackflies  on  a  large  scale.  The  stabbing  and  cutting  parts 
are  usually  short,  heavy  and  powerful,  though  in  one  genus, 
Pangonia,  the  proboscis  is  very  long,  enabling  the  fly  to  pierce 
flesh  and  suck  blood  while  hovering  in  the  air  and  to  pierce 
even   through   thick   clothing.     Most   of   the  species   are   very 


486 


OTHER  BLOOD-SUCKING  FLIES 


-labr.ep. 
hyp. 

Fig.  225.  Mouthparts  of  a  tabanid;  hyp. 
hypopharynx;  lab.,  labium;  label.,  labellum 
labr.  ep.,  labrum-epipharynx ;  mand.,  mandible 
max.,  maxilla;  max.  p.,  maxillary  palpus. 


deliberate  and  persistent  in  their  feeding  and  are  not  easily  dis- 
turbed when  they  have  begun  to  suck  blood.  The  thorax  is 
relatively  long,  and  the  wings  are  large  and  expansive  and  usually 
held  at  a  broad  angle  to  the  body,  as  shown  in  Fig.  227.  The 
markings  of  the  wings  usually  give  the  easiest  means  of  identi- 
fication of  the  genera.  Of 
the  four  most  important 
genera  as  human  pests, 
Tahanus  (Fig.  224)  is  of 
.large  size  and  has  clear 
or  smoky  wings,  with  no 
spots  or  a  few  small  scat- 
tered ones ;  Pangonia 
(Fig.  226)  also  has  clear 
or  smoky  wings  but  can 
be  distinguished  by  the 
long  proboscis;  Hcematopota  is  of  moderate  size  and  has  wings 
with  profuse  scroll-like  markings;  and  Chrysops,  the  species  of 
which  are  often  small,  even  smaller  than  a  housefly,  has  a  con- 
spicuous black  band  on 
the  wing  (Fig.  227). 

Life  History. — All  the 
tabanids  breed  in  water 
or  in  damp  places.  The 
eggs  (Fig.  224C),  several 
hundred  in  number,  are 
laid  in  definitely  shaped 
masses  on  the  leaves  of 
marsh  or  water  plants, 
on  the  leaves  or  twigs 
of     trees      overhanging 

water,    or   in    crevices   of        Fig.    226.     A  long-beaked  tabanid,    Pangonia 
rocks   alons  the   sides  of    f^^VvMU,  of  eastern  Africa.      X  2.     (After  Castel- 
_,,  lani  and  Chalmers.) 

streams.     The  eggs  are 

white  when  laid,  but  soon  turn  dark.  They  are  deposited  during 
the  summer  and  under  favorable  circumstances  hatch  in  from  five 
to  seven  days.  The  newly  hatched  larvae  fall  into  the  water  or 
to  wet  ground  or  decaying  vegetation  such  as  occurs  around  the 
edges  of  marshes,  in  sphagnum  bogs,  in  decaying  logs,  etc.  The 
larvae  (Fig.  224D)   are  cylindrical  legless  creatures,   pointed  at 


TABANIDS   AND    DISEASE  487 

each  end,  and  with  a  number  of  spines  or  warts  on  the  body. 
They  are  voracious  feeders  and  prey  upon  various  soft-bodied 
animals  which  they  find  in  the  water  or  mud  in  which  they  live, 
and  are  not  averse  to  the  practice  of  cannibalism  if  food  is  scarce. 
The  larvae  grow  rapidly  during  the  remainder  of  the  summer,  but 
remain  inactive  and  with  httle  or  no  growth  during  the  winter. 
In  the  spring  they  complete  their  development  and  creep  out  to 
drier  ground  to  pupate.  The  pupa  (Fig.  224E)  often  resembles 
the  chrysalis  of  a  butterfly  in  form.  The  adults  of  the  species 
of  temperate  climates  emerge  after  two  or  three  weeks,  but  King 
states  that  tabanids  in  the  Sudan  exist  as  pupae  only  six  to  eight 
days.  The  whole  life  history  of  species  of  temperate  climates 
therefore  occupies  about  a  year,  but  it  is  shorter  in  tropical  species, 
in  which  there  are  probably  several  broods  a  year. 

The  adult  flies  are  strictly  diurnal,  and  are  often  active  in  the 
clear  sunlight  of  a  summer  day,  though  many  forest-dwelling 
forms,  e.g.,  the  deerflies,  Chrysops,  prefer  shade.  They  do  not 
go  in  swarms  as  do  many  other  biting  insects  but  are  usually 
soUtary  in  habit.  On  account  of  their  powerful  wings  they  are 
sometimes  found  at  considerable  distances  from  their  breeding 
places.  As  remarked  before,  only  the  females  are  blood-suckers; 
the  males,  and  very  probably  the  females  to  some  extent  also, 
feed  on  plant  juices,  the  dew  of  leaves  which  hold  a  little  organic 
matter  in  solution,  excretions  of  insects,  etc.  Gadflies  collect 
near  pools  and  skim  over  the  surface  of  the  water,  the  under  side 
of  the  body  often  touching  the  water.  Portchinsky,  in  Russia, 
has  devised  a  means  of  trapping  the  flies,  based  on  this  habit 
(see  p  489) 

Tabanids  and  Disease.  —  Although  tabanids  are  not  known 
to  serve  as  the  intermediate  hosts  of  any  disease-causing  pro- 
tozoans, they  have  been  shown  to  be  efficient  as  mechanical 
disseminators  of  various  disease  germs,  being  especially  dangerous 
in  this  respect  on  account  of  their  intermittent  feeding.  It  is 
quite  common  for  them,  having  been  disturbed  while  feeding  on 
one  animal,  to  continue  their  meal  on  another. 

Surra,  an  important  disease  of  horses  in  southeastern  Asia  and 
Madagascar,  caused  by  a  trypanosome,  is  transmitted  in  this 
manner,  and  also  El  debab,  a  trypanosome  disease  of  camels. 
Other  trypanosome  diseases  of  animals,  normally  transmitted 
by  tsetse  flies,  can  be  transmitted  experimentally  by  tabanids, 


488  OTHER  BLOOD-SUCKING  FLIES 

but  only  immediately  after  the  infective  feed.  Human  trypano- 
some  diseases  have  been  suspected  of  being  transmitted  likewise, 
but  there  is  yet  no  proof  that  this  takes  place. 

The  most  important  disease  disseminated  by  tabanids  is  an- 
thrax. This  is  a  bacterial  disease  to  which  nearly  all  herbivorous 
animals  and  man  are  susceptible,  and  which  is  very  destructive, 
sometimes  killing  over  75  per  cent  of  its  victims.  The  bacilli 
which  cause  the  disease  gain  entrance  to  the  body  either  through 
abrasions  of  the  skin  to  the  blood,  through  spores  in  the  air  to 
the  lungs,  or  through  contaminated  food  to  the  intestine.  The 
bacilli  have  been  found  in  the  alimentary  canal  of  tabanids 
which  have  fed  on  dying  or  dead  victims,  and  animals  inoculated 
with  these  bacilli  died  of  anthrax.  That  these  flies  could  trans- 
mit the  disease  not  only  when  crushed  so  that  the  contents  of  the 
digestive  tract  could  contaminate  the  wound,  but  also  by  their 
bites,  has  been  stated  many  times,  and  has  recently  been  observed 
in  China  under  conditions  which  placed  it  beyond  doubt.  The 
method  of  transmission  is  purely  mechanical  and  probably  oc- 
curs only  when  a  fly  which  has  been  feeding  on  a  diseased  animal 
finishes  its  meal  on  a  healthy  animal  or  on  a  human  being,  the 
disease  germs  adhering  to  the  mouthparts  long  enough  to  be 
transferred  to  the  new  animal.  The  stable-flies,  Stomoxys,  and 
other  biting  flies  which  will  attack  two  or  more  animals  in  quick 
succession  are  equally  as  dangerous  as  anthrax  carriers. 

Tabanids  have  often  been  accused  of  causing  diseases  similar 
to,  if  not  identical  with,  oriental  sore.  In  the  intestines  of  vari- 
ous tabanids  there  exist  flagellate  parasites  belonging  to  the 
genus  Herpetomonas,  and  it  is  believed  that  if  these  should  ac- 
cidentally gain  entrance  to  the  flesh  of  a  human  being  by  contami- 
nation of  the  puncture  made  by  the  host  fly,  they  might  assume 
the  form  of  Leishman  bodies  and  multiply  to  a  sufficient  extent  to 
cause  a  local  sore.  Obviously  such  implanted  parasites  would 
be  permanently  side-tracked,  and  would  stand  little  chance  of 
ever  being  released  by  a  fly  of  the  species  in  which  they  nor- 
mally live.  Such  a  theory  is  proposed  to  explain  the  sporadic 
cases  of  leishmaniasis  of  the  skin  which  occur  in  Panama  and 
other  places,  and  which  are  usually  reported  to  develop  at  the 
site  of  a  horsefly  bite..  In  Sao  Paulo,  Brazil,  a  form  of  leish- 
maniasis is  very  common  among  forest  workers,  even  in  wild 
uninhabited  regions.     The  fact  that  the  disease  is  contracted 


CONTROL    OF    TABANIDS  489 

only  by  men  who  spend  the  day  in  the  forest,  and  is  most  prevalent 
in  May  and  June,  a  time  corresponding  to  the  appearance  of 
many  tabanids,  points  strongly  to  these  insects  as  the  carriers 
of  the  infection,  since  they  are  the  only  diurnal  insects  exclusively 
found  in  forest  regions.  The  forest  leishmaniasis  of  Paraguay 
may  also  be  due  to  tabanids. 

In  one  other  case  a  tabanid  is  implicated  in  the  spread  of  a 
disease.  In  the  tropical  jungles  of  Africa  certain  species  of 
Chrysops  locally  known  as 
mangrove  flies,  serve  as  in- 
termediate hosts  for  filarial 
worms.  Leiper  and  other 
investigators  have  found 
that  the  larvae  of  the  loa 
worm,  Loa  loa,  w^hich 
swarm  in  the  peripheral 
blood  of  the  host  in  the 
daytime      only,      undergo 

rapid   development   in   sev-  Fig.  227.     A  deerfly,  Chrysops  callidus. 

eral     Chrysops,     especially  ^   ' 

C  dimidiata  and  C.  silacea  (see  p.  309). 

It  has  recently  been  shown  by  Francis  that  tularemia,  a  rodent 
disease  of  western  United  States,  caused  by  Bacterium  tularense, 
and  transmissible  to  man,  may  be  transmitted,  and  probably 
commonly  is,  by  the  deerfly,  Chrysops  discalis.  These  flies  are 
infective  from  a  few  seconds  to  at  least  fourteen  days  after  biting 
an  infective  rabbit. 

Control.  —  Prevention  of  bites  from  tabanids,  especially  dur- 
ing an  epidemic  of  anthrax,  or  where  diseases  believed  to  be 
transmitted  by  tabanids  are  prevalent,  is  important.  Practi- 
cally the  only  means  that  can  be  employed  is  the  use  of  repellents, 
as  for  other  insect  pests  (see  p.  455).  According  to  Herms,  re- 
pellents efficient  against  tabanids  usually  contain  fish  oil. 

In  a  recent  publication  Por.tchinsky,  a  Russian  entomologist, 
having  found  that  tabanids  have  the  peculiar  habit  of  skimming 
over  pools,  touching  the  lower  side  of  their  bodies  to  the  surface, 
advised  the  conversion  of  such  pools  into  traps  by  pouring  oil 
on  them  to  produce  a  surface  film,  so  that  the  insects  would  be 
caught  in  it,  and  the  spiracles  (openings  of  the  tracheae  through 
which  air  is  absorbed)  closed  up.     In  an  experiment  which  he 


490  OTHER  BLOOD-SUCKING  FLIES 

performed  in  a  pool  with  a  surface  of  a  little  over  a  square  yard, 
he  caught  in  five  days  1260  male  and  258  female  Tabanus,  and 
416  male  and  33  female  Chrysops.  This  ''  pool  of  death  "  was 
literally  studded  with  "  floating  islands  of  dead  tabanids." 
The  flies  are  said  to  visit  the  pools  even  after  sucking  blood. 
Portchinsky  suggests  the  construction  of  traps  of  this  nature  in 
pastures  where  tabanids  are  troublesome,  fencing  them  in,  of 
course,  to  prevent  the  stock  from  getting  access  to  them. 

From  the  solitary  nature  of  the  flies,  and  the  great  variety  of 
breeding  places  which  may  be  selected,  it  is  obviously  impossible, 
in  most  cases,  to  exterminate  tabanids  during  their  early  stages. 
Natural  enemies  probably  do  much  to  limit  their  numbers; 
fishes  and  large  carnivorous  aquatic  insects  prey  upon  the  larvae, 
and  birds  and  hornets  on  the  adults.  Hine  describes  seeing 
bald-faced  hornets,  Vespa  maculata,  capture  and  cut  to  pieces 
horseflies  which  were  too  large  for  them  to  carry. 

Tsetse  Flies 

Next  to  the  mosquitoes  the  tsetse  flies  are  the  most  important 
of  the  biting  flies.  The  history  and  destiny  of  the  African  con- 
tinent has  been  and  will  be  very  largely  controlled  by  these 
insects.  As  far  as  their  own  biting  power  is  concerned,  tsetse 
flies  are  of  little  importance;  their  bites  are  less  painful  than  are 
those  of  many  other  biting  flies  of  similar  size.  It  is  in  the  role  of 
carriers  of  trypanosome  diseases  that  they  gain  their  importance. 
Not  only  the  two  or  possibly  three  forms  of  human  sleeping  sick- 
ness, but  also  a  large  number  of  deadly  trypanosome  diseases  of 
animals  are  transmitted  by  these  insects.  The  native  wild  ani- 
mals of  Africa  are  largely  immune  to  these  diseases  and  serve  as 
a  reservoir  for  them,  but  domestic  animals  and  man  succumb  in 
large  numbers,  in  fact  to  such  an  extent  that  some  parts  of  Africa 
are  uninhabitable,  and  in  other  parts  it  is  impossible  to  keep 
domestic  animals  of  any  kind.  The  abundant  and  varied  wild 
game  of  Africa,  particularly  the  numerous  species  of  antelopes, 
are  the  chief  natural  source  of  food  for  tsetse  flies,  and  since  the 
flies  serve  as  intermediate  hosts  for  the  trypanosomes  harbored 
by  the  wild  game,  it  is  obvious  that  when  man  or  domestic  ani- 
mals are  bitten  by  these  flies  they  are  in  great  danger  of  being 
inoculated  with  one  or  more  species  of  trypanosomes. 


TSETSE    FLIES 


491 


Fig.    228. 
position. 


Tsetse   fly   in   resting 
X  4.     (After  Austen.) 


General  Form.  —  The  tsetse  flies  (Fig.  228)  are  elongate,  dark 

brown  or  yellowish  brown  flies,  some  species  no  larger  than  an 

ordinary  housefly,  others  larger  than 

blowflies.  They  are  usually  in- 
cluded as  an  aberrant  group  of  the 

housefly  family,  Muscidse,  but  from 

other  members  of  the  family  they 

differ  in  a  number  of  striking  ways, 

especially  in  the  manner  of  repro- 
duction, and  in  form  of  the  larva. 

They  constitute  the  genus  Glossina 

which  contains  15  species  and  has 

no  very  close  allies;  some  species 

are  of  very  wide  distribution,  while 

others  are  local  or  very  rare.  Tsetses 

can   most   easily   be   distinguished 

from  other  flies  by  their  position 

when  at  rest  (Fig.  228) ;  their  wings 

are  folded  flat,  one  directly  over  the  other,  straight  down  the 

back,  like  the  blades  of  a  pair  of  scissors,  while  the  proboscis 
projects  horizontally  in  front  of  the  head. 
Beyond  these  characteristics  there  is  noth- 
ing strikingly  distinctive  about  a  tsetse  fly, 
and  it  is  therefore  diflftcult  for  anyone  who 
is  not  thoroughly  familiar  with  it  to  identify 
it  on  the  wing.  The  darting  manner  of 
flight  and  buzzing  sound  are  said  to  be 
quite  diagnostic  when  one  is  once  familiar 
with  them.  When  the  flies  are  caught  and 
examined,  however,  there  are  a  number  of 
good  identification  marks.  Most  charac- 
FiG.   229.     Head  and  teristic,   perhaps,   is    the    arrangement    of 

mouthparts  of  tsetse  fly;  r»rkrvs 

ant.,  antenna;    ep.,  epi-  the  mouthparts  and   antennae  (i^ig.  229). 
pharynx;     hyp.,     hypo-  j^c  proboscis  consists  of  a  bulblike  base 

pharynx;     palp.,    palpus;        ,  .   ,     .  ^.  ,  i        ,  ,      <.. 

lab.,  labium;  label.,  label-  which  IS  contmued  as  a  slender  shatt,  com- 
lum;  sp  spiracle.  (After  posed  of  a  grooved  lower  lip  with  two 
needle-Uke  puncturing  organs  within  it,  one 
of  which,  the  hypopharynx,  contains  a  delicate  tube  for  carrying 
the  salivary  juices.  The  proboscis  proper  is  ensheathed  in  the 
maxillary  palpi  which  are  so  grooved  as  to  conceal  entirely  the 


-.-label. 


492 


OTHER  BLOOD-SUCKING  FLIES 


Fig.  230.  Hypo- 

pygium    of  male 

tsetse    fly.  (After 
Alcock.) 


mouthparts  when  the  latter  are  not  in  use,  and  it  is  thus  the  palpi 
alone  that  are  seen  when  the  long  blunt-tipped  proboscis  is  ob- 
served. The  characteristic  form  of  the  antennae  is  shown  in 
Fig.  229.  The  thorax  is  relatively  large  and 
quadrangular,  with  a  characteristic  pattern 
which  is,  however,  inconspicuous  in  some 
species.  The  abdomen  may  be  nearly  uniform 
dark  brown,  or  pale  brown  banded  with  a 
dusky  color.  The  male  has  a  large  oval  swell- 
ing on  the  under  side  of  the  last  segment  of 
the  abdomen,  the  ^'  hypopygium  "  (Fig.  230), 
which  forms  a  good  distinguishing  mark  be- 
tween the  sexes. 
Distribution,  Habits,  etc.  —  Tsetse  flies,  fortunately,  are  lim- 
ited in  their  distribution  to  the  middle  portion  of  the  African 
continent  from  south  of  the  Sahara  Desert  to  the  northern  borders 
of  British  South  Africa  (Fig. 
231,  =  ).  One  species  occurs 
in  the  southwestern  corner 
of  Arabia.  Tsetses  are  by 
no  means  evenly  distributed 
over  this  great  area,  but  are 
limited  locally  to  ''fly-belts," 
chiefly  along  rivers  and  at 
the  edges  of  lakes.  All  the 
factors  which  cause  the 
"  patchy "  distribution  of 
tsetses  are  not  known;  there 
are  cases  where  close  limita- 
tion to  certain  areas  cannot 
be  explained  by  any  known 
requirements  of  the  flies. 
Different  species  vary  in 
their  choice  of  habitats; 
Glossina  palpalis  (Fig.  236), 
the  carrier  of  Gambian  and 
seldom   found    more  than    30 


Fig.  231. 

flies. 


\\\ 
/// 


Approximate  ranges  of  tsetse 
(Compiled  from  Austen.) 

range  of  entire  genus  glossina 
range  of  g.  morsitans 
range  of  g.  ■palpalis 


Nigerian  sleeping  sickness,  is 
yards  from  the  edge  of  water 
where  a  sandy  bottom  and  overhanging  vegetation  is  abun- 
dant, though  it  follows  animals  and  man  for  a  few  hundred 
yards  from  such  positions.     This  species  is  found  only  in  shady 


HABITS  OF  TSETSE  FLIES  493 

places  and  where  there  is  great  humidity.  Glossina  morsi- 
tans  (Fig.  237),  the  fly  which  is  particularly  well  known  to  big- 
game  hunters  in  Africa  and  is  the  carrier  of  Rhodesian  sleeping 
sickness,  is  less  dependent  on  water,  and  in  fact  prefers  a  rather 
hot  and  fairly  dry  climate.  It  is  confined  to  open  brushy  country 
with  scattered  trees,  where  there  is  a  moderate  amount  of  shade 
for  cover.  It  is  never  found  either  in  dense  forest  or  in  open 
grass  land.  Most  other  species  of  tsetses  resemble  one  of  these 
two  species  in  choice  of  habitats,  though  few  if  any  are  as  inde- 
pendent of  water  as  is  G.  morsitans. 

Tsetses  are  diurnal  in  habits,  but  the  time  of  activity  varies 
with  the  species.  G.  palpalis  is  most  active  during  the  middle 
part  of  the  day  on  bright  days;  G.  tachinoides,  on  the  other  hand, 
is  especially  hungry  on  dull  days  and  early  in  the  morning;  G. 
morsitans  is  active  in  the  morning  and  afternoon,  but  usually 
disappears  at  midday;  G.  hrevipalpis  and  G.  longipennis  bite 
in  the  early  morning  from  sunrise  until  about  8  a.m.  and  in  the 
afternoon  from  4  p.m.  until  some  time  after  dark.  Both  the  last- 
named  species  are  attracted  by  lights  at  night,  and  enter  lighted 
railroad  coaches  passing  through  the  '^  fly-belts."  G.  palpalis, 
and  probably  other  species,  also,  seldom  rise  more  than  a  few  feet 
above  the  ground. 

It  has  been  the  universal  experience  of  collectors  of  tsetse 
flies  that  the  males  outnumber  the  females,  often  to  the  extent  of 
ten  or  more  to  one.  Yet  it  is  a  remarkable  fact  that  when  bred 
in  the  laboratory,  males  and  females  are  obtained  in  equal  pro- 
portions. Many  different  explanations  for  these  apparently 
contradictory  facts  have  been  proposed,  but  the  most  probable 
is  the  one  recently  brought  out  by  Lamborn,  based  on  his  ob- 
servations on  G.  morsitans  in  Nyasaland.  Lamborn  has  ob- 
served that  copulation  takes  place  after  a  rough  capture,  and 
that,  in  captivity  at  least,  females  even  in  an  advanced  state  of 
gestation  are  not  exempt  from  the  attacks  of  the  males,  although 
this  often  results  in  abortion.  In  nature,  therefore,  the  preg- 
nant females  would  necessarily  have  to  hide  to  avoid  the  males, 
and  so  would  be  less  likely  to  be  caught  by  a  casual  collector. 

Tsetses  show  marked  preference  for  certain  colors,  being  es- 
pecially attracted  to  blacks  or  browns,  and  repelled  by  white. 
The  dark  skin  of  negroes  is  selected  in  preference  to  pale  skin  to 
such  an  extent  that  a  white  man  is  seldom  troubled  when  ac- 


494 


OTHER  BLOOD-SUCKING  FLIES 


companied  by  natives.  Black  or  dark  clothes  are  preferred  to 
light  ones;  khaki  color,  however,  appears  to  be  particularly 
attractive  to  them.  Moving  objects  seem  to  attract  the  flies, 
and  they  are  said  to  follow  launches  when  moving,  though  they 
leave  them  alone  when  quiet. 

When  biting,  these  flies  spread  apart  their  front  legs,  lower  the 
proboscis  into  the  skin  and  begin  to  gorge.      The  abdomen  of 

an  unfed  tsetse  is  very 
flat  (Fig.  232A)  but  after 
30  or  40  seconds  of  feed- 
ing it  becomes  distended 
like  a  balloon,  some- 
times containing  over 
twice  the  weight  of  the 
fly  in  blood  (Fig.  232B). 
The  flies  do  not  feed  ex- 
clusively on  blood,  but 
also  suck  plant  juices 
and  show  definite,  selec- 
tive taste  for  various 
fluids  presented  to  them 
under  a  membrane,  according  to  experiments  by  Yorke  and 
Blacklock.  Both  warm-  and  cold-blooded  animals  are  sucked, 
but  flies  fed  only  on  a  cold-blooded  animal  (crocodile)  never 
produce  offspring.  It  has  been  thought  that  perhaps  water 
fowl  constitute  an  important  article  of  diet  for  tsetses,  but  in 
the  case  of  Glossina  morsitans,  at  least,  birds'  blood  proved 
rather  indigestible  for  them,  and  often  produced  a  clot  in  the 
digestive  tract,  resulting  in  abortion  in  female  flies.  In  the  case 
of  such  species  as  G.  palpalis,  however,  bird  blood  may  be  more 
easily  digested,  and  the  diurnal  habits  and  close  adherence  to 
the  vicinity  of  water  would  argue  in  favor  of  subsistence  on 
water  animals,  in  part  at  least.  On  the  other  hand,  the  habit  of 
many  species  of  frequenting  places  where  game  animals  come  to 
drink  or  browse  and  of  feeding  early  in  the  morning  and  at  even- 
ing is  apparently  an  adaptation  to  the  habits  of  such  hosts  as 
wild  game  animals.  Examination  of  the  stomach  contents  of 
wild  flies  usually  shows  a  preponderance  of  mammal  blood,  but 
Carpenter,  studying  G.  palpalis  in  Uganda,  often  found  that  a 
large  proportion  of  some  collections  of  flies  had  fed  on  reptiles, 


Fig.  232.     Glossina  morsitans  before   (A)    and 
after  (B)  feeding.    X  4.     (After  Austen.) 


LIFE  HISTORY  OF  TSETSE  FLIES 


495 


Fig.  233.  Newly 
born  larva  of  tsetse 
fly,  Glossina  palpa- 
lis.  X  5.  (After 
Roubaud.) 


especially  on  certain  large  lizards.  Lloyd  thinks  that  small  mam- 
mals and  birds  may  be  important  sources  of  food  for  tsetses,  for, 
though  these  animals  are  usually  able  to  avoid  attacks  by  the 
flies  during  their  time  of  activity,  many  of  the  nocturnal  species 
hide  during  the  day  in  the  same  places  frequented 
by  the  flies  and  would  then  be  easy  prey  for 
them. 

Life  History.  —  Tsetse  flies  differ  from  all 
others  of  their  family  in  their  remarkable  manner 
of  reproduction.  Not  only  do  they  not  lay  eggs, 
but  the  single  developing  larva  is  retained  within 
the  body,  being  nourished  by  special  glands  on 
the  walls  of  the  uterus.  The  larva  is  full  grown 
and  occupies  practically  the  entire  swollen  abdo- 
men of  the  mother  before  it  is  born.  The  proc- 
ess of  giving  birth  to  the  larva  is  very  rapid, 
occupying  only  a  very  few  minutes.  As  soon  as 
born  another  larva  begins  its  development,  etc. 
In  Glossina  palpalis  the  first  larva  is  born  three  or  four  weeks  after 
mating,  immediately  after  emergence  from  the  pupal  case,  and 
another  is  born  every  nine  or  ten  days  providing  the  temperature 
is  around  75°  or  80°  F.  and  food  is  abundant. 
There  is  little  data  on  the  total  number  of  young 
produced,  but  in  one  captive  fly  eight  larvae  were 
produced  in  13  weeks  and  only  one  egg  was  found 
left  in  the  body.  Pregnant  flies  often  abort  when 
disturbed  and  cases  are  known  in  which  the  larvae 
pupated  within  the  abdomen  of  the  mother,  to 
the  destruction  of  both  of  them. 

The  larva  (Fig.  233)  is  a  yellowish  white  crea- 
FiG.  234.    Pupa  ture,  about  one-third  of  an  inch  in  length,  with 
sina  paipaiis.     X  a  pair  of  dark  knoblike  protuberances  at  the  pos- 

5.     (Partly  after  ^^j-ior  end  of  the  body  between  which  are  the  res- 
Austen.)  .  .  .  T         1      1   •  1         •         ir  • 

piratory  openings.  It  immediately  hides  itself  in 
loose  soil  or  under  dead  leaves  in  the  place  where  it  was  deposited 
by  the  mother,  and  transforms  to  a  pupa  (Fig.  234).  The  pupa- 
tion takes  place  in  the  course  of  less  than  half  an  hour  in  soft  dry 
ground,  and  in  an  hour  to  an  hour  and  a  half  in  hard  or  damp 
ground.  After  pupation  the  color  begins  to  turn  dark  and  in 
four  hours  the  pupa  is  a  dark  purplish  brown  color.     It  is  shaped 


496  OTHER  BLOOD-SUCKING  FLIES 

more  or  less  like  a  small  olive,  and  has  at  the  tip  of  the  body  the 
blackish  knobs  which  are  so  characteristic  of  the  larval  stage  also. 
The  shape  and  size  of  the  knobs  and  of  the  notch  between  them 
are  good  distinguishing  marks  between  species.  The  duration 
of  the  pupal  stage  depends  on  the  dryness  of  the  soil,  temperature, 
exposure  to  sunlight,  etc.,  and  may  occupy  from  17  days  to  nearly 
three  months.  In  experiments  made  by  Lloyd  with  Glossina 
morsitans  the  pupal  stage  ranged  from  23  days  at  85°  F.  to  81  days 
at  70°.  Few  adults  emerged  at  temperatures  below  70°  or  above 
86°.  Little  is  known  about  the  reproductive  season,  but  it  is 
probable  that  reproduction  occurs  only  in  the  warm  part  of  the 
dry  season  in  cool  climates,  but  may  occur  to  a  varjdng  degree 
throughout  the  year  in  hot  climates. 

The  places  selected  for  depositing  the  eggs  vary  somewhat 
with  the  species,  but  all  species  select  dry,  loose  soil  in  shaded, 
protected  spots,  preferably  in  places  where  a  little  sunlight  will 
penetrate  for  a  short  time  each  day  and  where  scratching  birds 
cannot  easily  reach  them.  G.  palpalis  deposits  under  tree  trunks 
and  at  the  foot  of  various  species  of  trees,  especially  where  a 
dense  thicket  gives  a  protected  spot.  In  Sierra  Leone,  Yorke 
and  Blacklock  found  numerous  pupal  cases  at  the  foot  of  oil- 
palms  where  the  dense  foliage  of  the  lower  limbs  makes  approach 
difficult.  G.  morsitans  is  partial  to  cavities  in  trees  or  stumps, 
or  under  logs  or  branches  lying  a  few  inches  above  the  ground 
(Fig.  235).  The  length  of  life  of  tsetses  is  probably  less  than  a 
year.  Specimens  have  been  kept  in  the  laboratory  for  over  eight 
months. 

Tsetse  Flies  and  Disease.  —  As  remarked  before,  the  enormous 
importance  of  tsetse  flies  lies  in  their  r61e  as  carriers  of  trypano- 
somes.  The  effect  of  trypanosome  diseases  on  domestic  animals 
in  Africa  has  practically  excluded  these  aids  to  development  and 
civilization  from  some  parts  of  that  continent.  The  importance 
of  trypanosomes  to  man  in  Africa  is  discussed  in  Chap.  VI.  It 
is  sufficient  here  to  repeat  that  sleeping  sickness,  which  is  the 
final  stage  of  trypanosome  disease,  is  one  of  the  most  deadly,  if 
not  the  most  deadly,  disease  known.  Several  types  of  the  disease 
are  recognized;  the  most  widespread  Gambian  disease  is  caused 
by  Trypanosoma  gamhiense  and  in  nature  is  transmitted  chiefly 
if  not  exclusively  by  Glossina  palpalis.  The  mild  Nigerian  form 
of  the  disease  is  believed  to  be  a  mere  variety  of  the  Gambian 


TSETSE  FLIES  AND  SLEEPING  SICKNESS 


497 


disease  and  is  likewise  transmitted  by  G.  palpalis.  Rhodesian 
sleeping  sickness,  however,  is  transmitted  by  G.  morsitans.  It 
is  the  beUef  of  some  workers  that  the  Rhodesian  parasite  is  a 


Fig.  235. 


Typical  breeding  places  of  Glossina  morsitans  in  Rhodesia.     (From 
photographs  from  Kinghorn  and  Yorke.) 


mere  strain  of  the  trypanosome,  T.  brucei,  which  causes  nagana 
in  animals  and  which  also  is  transmitted  by  G.  morsitans.  The 
development  of  the  trypanosome  in  the  flies  and  the  mode  of 
transmission  is  discussed  on  p.  99. 


498 


OTHER  BLOOD-SUCKING  FLIES 


Glossina  palpalis  (Fig.  236)  is  a  large  dark  species  with  black- 
ish brown  abdomen  and  with  gray  thorax  having  indistinct  brown 
markings.  This  species  is  found  over  the  whole  of  West  Africa, 
from  the  Senegal  River  to  Angola,  and  east  to  the  upper  valley  of 
the  Nile  and  the  eastern  shores  of  the  central  lakes  (Fig.  231,  \\\). 
Its  range  is  thus  nearly  coincident  with  that  of  Gambian  sleeping 
sickness.  This  species,  more  than  any  other  except  possibly 
G.  tachinoides,  which  occurs  around  the  southern  border  of  the 
Sahara  Desert,  is  dependent  on  the  presence  of  water.  Its  natu- 
ral range  is  said  seldom  to  exceed  30  yards  from  the  edge  of  water, 
and  the  distance  that  it  will  follow  animals  or  man  is  not  more 


Fig.  236.     Glossina  palpalis,  carrier  of  Gambian  and  Nigerian  sleeping  sick- 
ness.      X  4.     (After  Austen.) 

than  a  few  hundred  yards.  Muddy,  reedy  sloughs  or  swamps 
are  not  frequented  by  this  fly,  but  rather  sandy-  or  gravelly- 
banked  streams  with  abundant  overhanging  vegetation.  In 
the  rainy  season  the  flies  extend  their  range  to  headwaters  which 
are  dry  during  the  remainder  of  the  year  and  retreat  again  with 
the  drying  up  of  the  water.  It  is  feared  that  this  species  may 
sometime  bridge  the  short  gape  between  the  headwaters  of  the 
Congo  and  the  Zambesi,  and  become  established  along  the  latter 
river  and  its  tributaries,  carrying  sleeping  sickness  with  it. 

This  fly  probably  feeds  naturally  on  a  number  of  different 
animals.     Wild    game,    especially    the    Situtunga    antelope,    is 


GLOSSINA  MORSITANS 


499 


utilized  to  a  large  extent,  and  the  habitats  of  the  flies  imply  that 
they  feed  considerably  on  water  animals.  According  to  Fiske 
the  crocodile  is  the  host  of  first  choice,  VaranuSy  a  lizard,  second, 
and  the  Situtunga  antelope  third.  Water  fowl  are  believed  to  be 
attacked  also.  Goats  are  remarkably  unattractive  to  the  flies. 
Data  concerning  the  life  history  has  already  been  given. 

Glossina  morsitans  (Fig.  237),  carrier  of  many  trypanosome 
diseases  of  animals  and  of  the  newly  arisen  and  still  narrowly 
Hmited  Rhodesian  sleeping  sickness,  is  the  most  widely  distrib- 
uted species  of  tsetse  fly,  occurring  all  the  way  across  Africa 


Fig.  237.     Glossina   morsitans,    carrier   of   Rhodesian   sleeping   sickness. 

(After  Austen.) 


X4. 


from  Senegal  to  southern  Sudan  and  Abyssinia  on  the  north, 
to  northeastern  Transvaal  and  Zululand  on  the  south  (Fig.  231, 
\\\).  This  is  also  the  best  known  species,  and  is  the  one  which 
has  attracted  to  itself  the  attention  of  big-game  hunters  in  Africa 
for  many  years.  It  is  sHghtly  smaller  than  G.  palpalis  and  much 
lighter  colored,  with  very  inconspicuous  markings  on  the  gray 
thorax,  and  with  more  or  less  distinct  dark  bands,  not  con- 
tinuous across  the  middle  line,  on  the  buff  colored  abdomen. 
As  remarked  elsewhere,  G.  morsitans  is  not  confined  to  the  im- 
mediate vicinity  of  water,  but  prefers  hot  dry  country,  covered 
with  bush  or  scattered  trees.     In  some  places  it  is  found  at  an 


500  OTHER  BLOOD-SUCKING  FLIES 

altitude  of  over  5000  feet,  but  usually  occurs  at  much  lower 
levels.  It  feeds  on  the  blood  of  almost  any  large  mammal  which 
comes  its  way.  It  was  long  supposed  that  the  fly  was  especially 
dependent  on  the  Cape  buffalo,  Bubalis  caffer,  as  it  undoubtedly 
was  before  this  animal  was  almost  exterminated  by  rinderpest, 
but  the  fly  is  certainly  able  to  exist  in  the  absence  of  the  buffalo, 
though  often  in  less  numbers  than  when  the  abundant  food  supply 
was  at  hand.  Baboons  are  said  to  be  relished  by  the  fly  in  some 
parts  of  Africa. 

Glossina  morsitans,  though  most  active  in  the  morning  and 
late  afternoon,  sometimes  bites  at  midday  and  even  after  dark, 
especially  on  warm  moonlight  nights.  The  habit  of  following 
moving  objects  is  especially  marked  in  this  species,  and  some 
observers  state  that  flies  have  followed  them  several  miles,  fre- 
quently alighting  on  the  ground  to  rest,  or  on  the  person  pursued, 
often  without  attempting  to  bite. 

The  reproduction  and  choice  of  breeding  places  of  this  species 
have  already  been  mentioned. 

Although  G.  palpalis  is  undoubtedly  the  normal  transmitter 
of  Gambian  sleeping  sickness  and  G.  morsitans  of  Rhodesian 
sleeping  sickness,  they  are  not  the  only  species  which  have  been 
found  capable  of  transmitting  these  diseases,  at  least  under  labo- 
ratory conditions.  G.  morsitans  has  been  found  ix>  be  able  to 
nurse  Trypanosoma  gamhiense  in  some  districts  but  not  in  others. 
G.  pallidipes,  which  resembles  G.  morsitans  but  is  larger,  and 
confined  to  southeastern  Africa,  can  be  experimentally  in- 
fected also. 

G.  tachinoides  is  suspected  of  carrying  sleeping  sickness  in  parts 
of  Nigeria  and  Togoland.  This  is  one  of  the  smallest  species, 
being  about  the  size  of  a  housefly.  It  has  very  distinct  bands  on 
the  abdomen,  and  is  browner  and  darker  than  G.  morsitans. 
It  is  found  around  the  southern  edges  of  the  Sahara  Desert  and 
in  southwestern  Arabia.  Its  habitats  are  practically  the  same 
as  those  of  G'.  palpalis  but  it  is  active  on  dull  days  and  early  in 
the  morning  when  the  latter  species  is  quiet.  It  frequently 
bites  after  dark,  also,  and  in  some  places  is  said  to  be  more 
troublesome  than  mosquitoes. 

Another  species  experimentally  able  to  transmit  human 
trypanosomes,  T.  gamhiense,  is  G.  brevipalpis,  of  South  Central 
and  East  Africa.     This  is  a  large  species  found  in  abundant 


CONTROL  OF  TSETSE  FLIES  501 

shade,  in  bush  mixed  with  creepers  and  young  trees  near  water 
courses.  Its  counterpart  in  the  more  northern  parts  of  East 
Africa  is  Glossina  longipennis,  a  large  warm-brown  species  with 
indistinct  markings.  G.  brevipalpis  is  said  to  be  desirous  of 
feeding  only  before  8.00  a.m.  and  after  4.00  p.m.  In  the  middle 
of  the  day  it  hides  under  leaves  or  grass  blades  near  the  ground, 
so  that  its  presence  would  never  be  suspected. 

To  sum  up  it  niay  be  said  that  while  there  is  much  variation 
in  the  susceptibility  of  different  species  of  tsetses  to  different 
trypanosome  infections,  so  that  one  or  a  few  species  come  to 
serve  as  the  usual  transmitters  of  any  particular  trypanosome, 
yet  other  species  cannot  be  definitely  excluded  as  carriers  with- 
out extended  experimentation.  Even  in  the  case  of  natural 
carriers  of  a  particular  trypanosome,  a  very  small  per  cent  of 
flies  are  found  naturally  infected,  and  not  more  than  a  few  per 
cent  can  be  infected  experimentally.  Moreover  it  is  evident 
that  a  single  species  of  fly  shows  marked  differences  in  recep- 
tivity to  infection  in  different  parts  of  the  range.  The  re- 
fractory nature  of  some  West  African  races  of  G.  palpalis  prob- 
ably accounts  for  the  absence  of  sleeping  sickness  in  Dahomey 
and  neighboring  states.  It  is  probable  that  climatic  conditions 
and  food  habits  play  a  leading  part  in  determining  susceptibility 
of  flies  to  trypanosome  infections. 

Control.  —  Attacks  of  tsetse  flies  can  be  avoided  to  some  ex- 
tent by  the  use  of  the  usual  insect  repellents  (see  p.  455),  by 
fly-proof  clothing  or  veils,  and  by  wearing  white  clothes.  When 
it  is  necessary  to  travel  through  fly-infested  places  where  sleeping 
sickness  occurs,  all  of  such  measures  should  be  adopted,  or, 
better  still,  the  fly-belts  should  be  passed  through  in  the  dark- 
ness of  night  when  the  insects  are  inactive.  Railroad  trains  and 
steamboats  passing  through  fly-belts  should  be  protected  by 
fly-proof  screens;  this  expedient  is  adopted  in  many  parts  of 
Africa  at  the  present  time. 

Extermination  of  tsetses  on  a  large  scale  is  a"  very  difficult 
matter,  but  locally  it  is  quite  feasible.  There  are  probably 
factors  influencing  the  distribution  of  the  flies  which  are  still 
unknown,  and  which  may  be  turned  to  account  in  destroying 
them. 

Clearing  away  of  brush  along  fly-infested  streams  in  the  case 
of  such  species  as  G.  palpalis  and  G.  tachinoides,  which  are  closely 


502  OTHER  BLOOD-SUCKING  FLIES 

confined  to  patches  of  brush  along  water  courses,  is  the  most 
valuable  measure  in  connection  with  their  local  destruction. 
As  said  before,  these  flies  seldom  go  over  50  yards  from  such 
brushy  borders  of  streams  except  when  following  prey,  in  which 
case  they  may  go  several  hundred  yards.  If  brush  is  cleared 
away  and  low  branches  of  trees  cut  out  for  a  distance  of  30 
yards  from  the  edge  of  water  in  the  vicinity  of  fords,  villages, 
washing  places,  etc.,  the  flies  quickly  disappear,  and  do  not  re- 
appear as  long  as  the  cleared  area  is  kept  clear.  The  effective- 
ness of  this  method  of  extermination  has  been  demonstrated 
especially  well  by  the  Portuguese  Sleeping  Sickness  Commission 
on  the  Island  of  Principe  where  tsetse  flies  were  almost,  though 
not  entirely,  exterminated  in  a  four  years'  campaign.  In  ad- 
dition to  clearing  margins  of  bodies  of  water,  the  beds  of  the 
water  courses  were  straightened  and  leveled  to  make  the  clear- 
ing easier,  and  forests  were  completely  cleared  away  on  a  large 
scale  where  they  seemed  to  harbor  tsetses.  In  addition  some  of 
the  men  employed  in  these  operations  wore  on  their  backs  black 
cloths  smeared  with  sticky  bird-lime,  thus  being  converted 
into  active  traps  for  capturing  flies.  Nearly  half  a  million  flies 
were  thus  caught,  and  the  number  caught  daily  gave  a  good  in- 
dex to  the  effectiveness  of  the  preventive  measures  being  used, 
and  must  of  itself  have  been  a  supplementary  means  of  destruc- 
tion which  was  of  value.  The  eradication  of  Glossina  morsi- 
tans  is  a  much  more  difficult  problem,  since  its  habitats,  though 
sharply  confined  to  "  belts,"  are  not  so  closely  limited  to  the 
edge  of  water,  and  are  therefore  more  difficult  to  clear.  Since, 
however,  the  areas  occupied  are  usually  not  over  a  few  square 
miles  at  the  most,  complete  deforestation  of  such  areas  when 
near  villages  or  highways  would  often  be  feasible. 

The  destruction  of  pupae  of  tsetse  flies  by  natural  enemies 
undoubtedly  aids  in  limiting  their  numbers,  but  the  instinct 
which  leads  tsetses  to  deposit  their  offspring  where  birds  cannot 
scratch  gives  the  pupae  a  high  degree  of  immunity  to  this  class 
of  natural  enemies  and  to  artificial  means  of  destruction.  The 
newly  deposited  larvae  are  covered  by  a  slimy  secretion  which 
apparently  protects  them  against  the  attacks  of  the  ants  which 
almost  always  abound  in  the  tsetse  breeding  places.  The  pu- 
pae are  attacked  by  parasitic  insects  (Fig.  238),  but  apparently 
not  to  a  sufficient  extent  to  seriously  reduce  their  numbers. 


CONTROL  OF  TSETSE  FLIES  503 

However,  five  species  of  Hymenoptera  and  two  of  Diptera  are 
known  to  parasitize  the  pupae  of  tsetse  flies.  It  is  possible  that 
some  of  these  insects  could  be  successfully  exploited.  The 
adults  of  G.  morsitans  are  attacked,  according  to  Lamborn,  by 
a  species  of  dragon-fly,  Orthetrum  chrysostigma, 
which  persistently  pursues  them  and  diligently 
searches  the  vicinity  of  men  and  animals  for 
them.  Elimination  of  breeding  places  is  the 
only  feasible  method  for  exterminating  tsetses 
in  their  early  stages. 

Constructive  measures  should  follow  the  de- 
structive ones,  such  measures,  for  instance,  as  ^^ 
the  cultivation  of  unfavorable  plants  and  en-  case  of  Giossina 
couragement  of  natural  enemies.  Following  are  J^°^«*^^«'  showing 
summarized  briefly  the  methods  of  fighting  of  a  small  chaicid 
tsetses  advised  by  Bagshawe:  parasite.  x4.  (Af- 

/   X      1        •  <-    n      ■    r  11         1  1    .  *^^  Waterston.) 

(a)  clearing  of  liy-miested  brush,  and  its  re- 
placement by  citronella  grass  or  other  plants  noxious,  or  at  least 
not  favorable,  to  the  flies; 

(6)  filling  up,  straightening  out  and  draining  of  pools  and 
water  courses  where  possible; 

(c)  destruction  of  main  food  animals,  if  found  feasible  and 
possible.  (The  wholesale  destruction  of  wild  game  is  not  ad- 
vised by  Bagshawe.) 

(d)  encouragement  and  introduction  of  natural  enemies,  and 
investigation  of  food  habits  of  possible  enemies  among  birds 
and  bats.  The  black  drongo,  Dicrurus  ater,  and  the  small  bee 
eater,  Melittophagus  meridionalis,  are  known  to  feed  on  the 
adult  flies. 

(e)  collection  and  destruction  of  pupae  or  adult  flies.  This 
can  be  facilitated  by  creating  artificial  sites  for  depositing  lar- 
vae to  which  the  flies  will  be  attracted.  Natives  in  Sudan  arc 
said  to  use  gourds  filled  with  blood  for  capturing  flies  to  be 
turned  loose  to  torture  the  stock  of  enemy  tribes.  Other  traps 
have  been  devised  also,  among  which  should  be  mentioned  the 
black  bird-lime  cloths  already  described  as  being  used  on  the 
Island  of  Principe. 

Some  workers  have  advocated  the  wholesale  destruction  of 
wild  game  animals  in  parts  of  Africa  where  deadly  trypanosome 
diseases  occur,  in  the  hope  that  in  this  way  the  natural  reservoirs 


504  OTHER  BLOOD-SUCKING   FLIES 

of  the  disease  could  be  destroyed,  and  that  the  tsetse  flies  would 
disappear  if  their  main  source  of  food  were  cut  off. 

Domestic  animals  are,  however,  quite  as  suitable  for  tsetse 
flies  to  feed  upon  as  are  wild  game  and  there  is  ample  reason  to 
believe  that  the  flies  would  be  able  to  subsist  on  small  forest 
mammals,  birds,  crocodiles,  etc.,  in  the  absence  of  other  food. 
Even  if  all  the  wild  game  were  destroyed,  and  domestic  animals 
excluded  for  many  years,  enough  flies  would  survive  to  reestab- 
lish the  scourge  with  the  subsequent  introduction  of  domestic 
animals.  The  destruction  of  the  rich  and  varied,  and  indeed 
unique,  wild  life  of  Africa  is  a  measure  so  radical,  so  contrary 
to  our  present  growing  determination  to  save  the  irreplaceable 
handiworks  of  nature,  and,  to  be  sure,  so  inhuman,  that  it  cannot 
be  advocated  or  even  tolerated  until  absolutely  proved  to  be  an 
effective,  and  the  only  effective  measure. 

Stable-Flies   {Stomoxys)  and  Their  Allies 

Belonging  to  the  family  Muscidse  in  company  with  the  house- 
flies,  blowflies  and  tsetse  flies,  are  a  number  of  other  biting  flies, 
most  important  of  which  are  the  stable-flies,  Stomoxys,  especially 


Fig.  2.39,     Stable-fly,  Stomoxys  calcitrans.      X  5. 

the  common  species,  S.  calcitrans  (Fig.  239),  which  makes  itself 
annoying  and  often  dangerous  in  nearly  every  part  of  the  world. 
It  is  chiefly  a  persecutor  of  domestic  animals,  but  is  very  willing 
to  attack  man  when  opportunity  is  offered. 

The  stable-fly  in  general  appearance  so  closely  resembles  the 
housefly,  Musca  domestica,  as  often  to  be  mistaken  for  it,  whence 


STABLE-FLIES 


505 


■*-  kxb. 
cp. 

Fig.  240.    Head  and  mouthparts 
of  stable- fly,  Stomoxys   caldtrans; 


4abe^'^ 


the  frequent  statement  that  houseflies  sometimes  bite.  They 
differ,  however,  in  several  ways.  The  stable-fly  is  more  robust, 
browner  in  color,  rests  with  the  wings  spread  at  a  broader  angle, 
and  has  a  narrow,  pointed  shining-black  proboscis  (Fig.  24G) 
which  is  quite  different  from  the  blunt  fleshy  proboscis  of  the 
housefly. 

The  mouthparts  (Fig.  240)  differ  from  those  of  many  other 
biting  flies  in  that  the  lower  lip,  which  usually  merely  forms  a 
sheath  for  the  piercing  mouthparts, 
is  itself  a  piercing  organ.  It  is  bent 
at  nearly  right  angles  under  the  head 
so  that  it  projects  straight  forward, 
being,  therefore,  fixed  to  the  head 
like  a  bayonet  to  a  rifle.  The  short 
basal  segment  is  movable  and  mus- 
cular, and  is  used  to  manipulate  the 
proboscis  itself.  The  latter  has  at 
its  tip  rasplike  spines  which  aid  in 
perforating    the    skin    of    the    host. 

Inside  the  groove  in  the  lower  lip  is    ^nt.,  antenna;    ar.,   arista   of  an- 

the  labrum  and  hypopharynx  which  t^::;;:!:',:^^^;^^^:^^. 
together  form  a  sucking  tube.     The  lum:  max.  p.,  maxillary  palpus, 
maxillary  palpi,  which  form  enclosing   ^    *^^    ^rms.) 
sheaths  for  the  proboscis  in  tsetse  flies,  are  less  than  half  the 
length  of  the  proboscis  in  Stomoxys. 

The  stable-fly  is  commonly  beheved  to  breed  in  manure,  and 
gains  its  name  from  the  frequency  with  which  it  is  found  about 
stables,  presumably  having  been  bred  in  manure.  As  a  matter 
of  fact,  the  presence  of  stable-flies  about  stables  is  due  to  the 
presence  there  of  animals  —  horses,  cattle,  etc.,  —  on  which  they 
feed.  The  breeding  place  which  is  most  preferred  is  moist, 
decaying  straw  or  rotting  vegetable  matter.  According  to  Herms, 
the  very  best  breeding  places  are  afforded  by  the  left-over  hay, 
alfalfa  or  grain  in  the  bottoms  of,  or  underneath,  out-of-door 
feed  troughs  in  connection  with  dairies.  In  this  soggy,  fermented 
material  practically  pure  cultures  of  Stomoxys  larva?  may  be  ob- 
tained. 

The  eggs  of  Stomoxys  (Fig.  241)  are  banana-shaped  white 
objects  about  one  mm.  in  length,  curved  on  one  side  and  flat 
on  the  other,  with  a  groove  on  the  flat   side.     They  are  de- 


506 


OTHER  BLOOD-SUCKING  FLIES 


Fig.    241.     Eggs  of     stable-fly, 

Stomoxys    calcitrans.  X  20.      Note 

eggs  natural   size   in  upper   corner. 
(After  Newstead.) 


posited,  sometimes  deep  in  the  decaying  material  selected,  in 
small  batches  of  from  two  to  half  a  dozen,  until  from  25  to  50  or 
more  are  laid;  there  are  a  number  of  such  depositions  made  by  a 
single  fly  during  her  hfe.     The  eggs  hatch  in  from  two  to  five 

days,  usually  three,  into  whitish, 
almost  transparent  footless  mag- 
gots (Fig.  242A)  very  similar  to 
those  of  the  housefly,  but  easily 
distinguishable  by  the  position  of 
the  posterior  stigmal  plates  (see 
Fig.  243).  The  larvae  mature  in  a 
minimum  of  from  12  days  to  over 
two  months,  usually  in  about  15  to 
20  days,  and  crawl  into  drier  por- 
tions of  the  breeding  material  to 
pupate.  The  pupae  (Fig.  242B)  are 
olive-shaped,  chestnut-colored  ob- 
jects, one-fourth  of  an  inch  in 
length.  With  favorable  temperatures  the  adult  fly  emerges  in 
from  six  to  ten  days,  but  this  period  may  be  much  prolonged 
by  cold  weather.  The  shortest  time  in  which 
a  stable-fly  may  develop  from  the  time  of 
egg-laying  is  about  three  weeks,  and  this  is 
extended  under  conditions  which  are  not 
ideal.  According  to  Herms'  experiments, 
the  average  length  of  life  of  stable-flies  is 
about  20  days.  They  sometimes  live  several 
months,  however. 

There  are  several  other  genera  and  species 
of  the  family  Muscidse  which  sometimes 
bite  man,  but  none  of  them  are  habitual 
feeders  on  human  blood,  and  they  are  hardly 
worthy  of  special  consideration.  They  all 
resemble  Stomoxys  in  general  appearance, 
though  some,  notably  the  common  hornfly, 
Hcematohia  serrata  (or  Lyperosia  irritans),  are  much  smaller.  Their 
life  histories  are  in  general  like  that  of  Stomoxys,  though  there  is 
some  variation  as  regards  choice  of  breeding  places.  Manure  of 
various  kinds  is  selected  by  some  species,  as  it  is  by  the  house- 
fly, much  more  than  in  the  case  of  the  stable-flies. 


Fig.  242.  Larva  (A) 
and  pupa  (B)  of  stable- 
fly,  Stomoxys  calcitrant 
X  4.    (After  Newstead.) 


STABLE-FLIES  AND  DISEASE  507 

Stomoxys  and  Disease.  —  Like  the  tabanids,  the  stable-flies 
are  intermittent  feeders,  i.e.,  they  frequently  leave  one  animal 
in  the  course  of  a  meal  if  disturbed,  to  finish  feeding  on  another. 
For  this  reason  they  are  of  importance  in  mechanically  trans- 
mitting blood  diseases. 

It  has  been  shown  that  the  trypanosome  of  sleeping  sickness, 
T.  gamhiense,  can  be  transmitted  by  interrupted  feeding,  and  a 
few  years  ago  Macfie  showed  that  the  Nigerian  strain  of  the 
parasite  could  go  through  at  least  part  of  its  development  in  the 
gut  of  the  black  stable-fly,  Stomoxys  nigra  (see  p.  98). 

More  serious  than  this  is  the  relation  of  stable-flies  to  anthrax 
(see  p.  488).  This  fatal  disease  of  domestic  animals  and  man  is 
caused  by  bacteria  which  live  long  enough  on  or  in  the  proboscis 
of  stable-flies  to  be  readily  transmitted  by  them  within  an  hour 
or  two  after  an  infective  feed.  The  biting  flies  of  this  or  other 
species  which  congregate  to  feed  on  sick  or  dying  animals  must 
be  looked  upon  as  a  serious  source  of  danger.  Other  diseases, 
such  as  foot-and-mouth  disease,  to  which  both  animals  and  man 
are  susceptible,  may  presumably  be  transmitted  in  like  manner 
by  these  flies,  though  no  proof  of  it  has  yet  appeared. 

In  1912  and  1913  several  American  workers,  among  them  Dr. 
M.  J.  Rosenau,  of  the  U.  S.  Public  Health  Service,  adduced  the 
theory  that  the  stable-fly,  Stomoxys  calcitrans,  was  responsible 
for  the  transmission  of  infantile  paralysis,  and  the  theory  was 
apparently  supported  by  some  facts  in  the  epidemiology  of  the 
disease  (though  contradicted  by  others),  and  by  carefully  con- 
ducted experiments.  In  subsequent  experiments,  however,  by 
the  same  and  other  workers,  the  results  have  been  uniformly 
negative,  and  in  the  meantime  much  data  has  been  collected  to 
show  that  this  terrible  disease,  which  reached  unprecedented 
proportions  in  New  York  City  and  vicinity  during  the  past  year 
and  terrorized  the  entire  United  States,  is  transmitted  by  con- 
tagion, and  not  through  the  agency  of  any  particular  insects. 
It  cannot  be  said  that  the  disease  is  never  transmitted  by  biting 
flies,  or  by  ordinary  houseflies,  but  that  insects  are  not  the  main 
or  even  important  factors  in  the  spread  of  the  disease  is  now  a 
fairly  well-established  fact. 

Control.  —  Control  of  the  stable-flies  and  of  allied  species  of 
biting  flies  depends  almost  entirely  on  the  elimination  of  their 
favorite  breeding  places.     In  the  case  of  Stomoxys,  which  is  the 


508  OTHER  BLOOD-SUCKING  FLIES 

most  important  of  this  group  of  biting  flies,  preventive  measures 
are  fairly  easy.  The  drying  out,  burning,  or  burying  of  waste 
vegetable  matter,  such  as  piles  of  weeds,  wet  hay,  lawn  clippings, 
waste  vegetable  matter  in  garbage  heaps,  etc.,  eliminate  the  main 
breeding  places.  Poorly  constructed  hay  stacks,  around  which 
there  is  a  good  deal  of  loose  hay  which  becomes  soggy  and  de- 
cays, are  breeding  centers  for  the  flies.  Stacks,  when  needed, 
should  be  constructed  with  evenly  rounded  top  and  vertical  sides; 
but  a  better  way,  when  possible,  is  to  bale  hay  or  straw  and  store 
it  in  dry  places.  Manure  especially  when  mixed  with  straw  is 
utilized  by  stable-flies  in  lieu  of  better  breeding  places,  but  the 
principal  manure-breeder  is  the  housefly,  Musca  domestica.  Ac- 
cording to  recent  work  by  the  U.  S.  Department  of  Agriculture, 
manure  can  be  treated  in  such  a  way  as  to  destroy  the  young 
stages  of  stable-flies  and  houseflies  without  injuring  its  fertilizing 
value.  A  mixture  of  ten  oz.  of  borax  and  12  oz.  of  crude  calcium 
borate,  (colemanite)  is  applied  to  ten  cubic  feet  (eight  bushels) 
of  manure,  the  manure  being  then  sprinkled  with  two  or  three 
gallons  of  water.  A  still  better  substance  to  apply  is  hellebore 
powder,  one-half  lb.  in  ten  gallons  of  water  to  eight  bushels  of 
manure.  An  excessive  quantity  of  the  powder  has  no  injurious 
action  on  the  fertilizing  power  of  the  manure,  as  has  an  excess  of 
borax. 


CHAPTER  XXVII 
FLY  MAGGOTS  AND   MYIASIS 

General  Account.  —  Disgusting  as  it  may  seem,  the  human 
body  is  attacked  not  only  by  the  numerous  adult  flies  discussed 
in  the  last  chapter,  but  is  subject  to  attacks  or  invasion  by  the 
maggots  or  larval  stages  of  some  species  of  flies.  Such  an  in- 
festation by  fly  maggots  is  commonly  known  as  myiasis,  intestinal 
myiasis  being  the  presence  of  fly  larvae  in  the  intestine,  cutaneous 
myiasis  in  the  skin,  etc. 

All  of  the  maggots  which  habitually  or  occasionally  parasitize 
man  belong  to  the  order  Diptera,  and  to  the  suborder  Orthor- 
rhapha,  in  which  the  larvae  have  very  small  and  indistinct  heads, 
and  the  pupse  are  inactive  oval  bodies  from  which  the  adults  emerge 
by  pushing  off  one  end,  like  a  cap  (see  p.  465  and  Fig.  209 A). 

Most  cases  of  myiasis  are  caused  by  flies  quite  closely  allied 
to  houseflies,  and  this  famous  transporter  of  germs  and  filth  is 
itself  occasionally  guilty.  The  identification  of  maggots  is  often 
a  difficult  matter  and  is  sometimes  impossible  without  rearing 
the  adult  insect.  Larvae  of  the  botfly  family,  (Estridae,  are  of 
various  shapes,  but  seldom  taper  evenly  from  the  posterior  to  the 
anterior  end;  the  body  has  a  leathery  covering  and  is  armed 
with  girdles  of  thornlike  spines.  Larvae  of  the  genus  Fannia 
(Fig.  253)  are  flattened,  and  have  very  characteristic  fleshy 
processes  along  their  sides.  Nearly  ah  other  maggots  causing 
myiasis  are  cylindrical,  whitish,  footless  creatures,  tapering  from 
the  broad  posterior  end  to  the  small  head,  and  are  difficult  to 
identify.  The  chief  characteristics  used  for  distinguishing  them 
are  the  number  and  form  of  the  mouth  hooks  (see  Fig.  251), 
and  the  nature  of  the  respiratory  openings  at  the  posterior  end 
of  the  abdomen.  These  openings  consist  of  two  '^  stigmal  plates," 
hardened,  yellowish,  eyelike  spots,  in  which  are  three  slits  or 
openings,  with  sometimes  a  button-like  mark  at  their  base. 
The  relative  position  of  the  stigmal  plates  to  each  other  and  to  the 
surface  of  the  larva,  and  the  form  of  the  slits,  whether  straight, 
curved  or  wavy,  and  whether  vertical  or  oblique,  are  some  of 

509 


510 


FLY  MAGGOTS  AND  MYIASIS 


the  characters  used  in  distinguishing  genera  and  species  of  fly 
maggots.     A  few  typical  forms  are  shown  in  Fig.  243. 

It  is  more  convenient  to  consider  the  different  types  of  myiasis 
according  to  the  way  in  which  the  larvae  attack  the  body  or  ac- 
cording to  parts  affected  than  according  to  the  families  and  genera 
to  which  the  flies  belong.     We  may  divide  the  various  flies 


LucUla  cae^ar(xso7 


t^astrophilaa  9p?(X2S) 


Oestrus   ovis  w^o? 


Fig.  243.  Posterior  stigmata  and  breathing  pores  of  various  maggots.  Note 
distance  apart  of  opposite  stigmal  plates,  form  and  position  of  spiracles,  pres- 
ence or  absence  of  button,  etc. 


causing  myiasis  into  four  groups :  (a)  those  in  which  the  larvge  live 
outside  the  body  and  suck  blood  by  puncturing  the  skin,  (h) 
those  in  which  the  larvae  develop  under  the  skin;  (c)  those  in 
which  the  eggs  or  young  larvae  are  deposited  in  wounds  or  in 
natural  cavities  of  the  body,  such  as  the  nose,  ears  and  vagina; 
and  (d)  those  which  live  in  or  pass  through  the  intestine  or  uri- 
nary passages. 


CONGO  FLOOR  MAGGOT 
Blood-Sucking  Maggots 


511 


A  number  of  species  of  flies  allied  to  the  blowflies  are  known  to 
deposit  their  offspring  in  the  nests  of  birds,  where  the  maggots 
attach  themselves  to  the  nestlings  and  suck  blood.  The  only- 
species  of  fly  in  which  the  larva  sucks  blood  by  puncturing  the 
skin  of  man,  however,  is  the  Congo  floor  maggot,  Aucheromyia 
luteola  (Fig.  244),  found  throughout  tropical  Africa  south  of  the 
Sahara  Desert.     Its  range  closely  coincides  with  that  of  the 


Fig.  244.     Congo  floor  maggot  and  adult  female  fly,  Aucheromyia  luteola. 
A,  X  3;   B,  X  4.     (After  Manson.) 

Negro  and  Bantu  races  of  men;   it  does  not  occur  in  countries 
inhabited  by  Arabs  and  Berbers. 

The  adult  fly  (Fig.  244A)  resembles  the  blowfly,  to  which  it  is 
nearly  related.  The  color,  however,  is  different,  being  a  dirty- 
yellowish  brown  with  the  tip  of  the  abdomen  rusty  black.  This 
fly  can  usually  be  observed  in  shady  places  about  human  habi- 
tations, preferring  the  vicinity  of  latrines;  it  feeds  principally 
on  rotting  fruits  and  on  excrement.  The  female  lays  her  eggs 
during  the  daytime  in  dust  or  debris  in  shady  places,  especially 


512  FLY  MAGGOTS  AND  MYIASIS 

on  the  floors  of  native  huts.  The  fly  is  said  by  Roubaud  to  make 
a  furrow  in  the  dust  with  her  abdomen  while  running  on  the 
ground,  feeUng  for  breaks  or  cracks  in  which  to  deposit  her  eggs. 
Having  found  such  a  spot  she  forces  her  abdomen  into  it  and 
deposits  usually  a  single  egg,  then  seeks  a  new  crack,  deposits 
another  egg,  etc.,  until  the  whole  number  of  from  30  to  80  eggs 
has  been  disposed  of.  The  eggs,  the  development  of  which  is 
favored  by  dry  surroundings,  hatch  in  a  few  days.  Within  four 
or  five  hours  after  emergence  the  larvae  are  ready  to  suck  blood  if 
opportunity  presents  itself,  but  they  are  able  to  live  nearly  a 
month  without  food,  remaining  buried  an  inch  or  so  in  the  dust 
of  floors.  They  can  always  be  collected  by  digging  with  the  point 
of  a  knife  in  cracks  in  the  earth  under  sleeping  mats.  Roubaud 
collected  100  larvae  in  half  an  hour,  many  of  them  filled  with 
blood,  in  a  hut  where  a  dozen  children  slept. 

The  maggots  (Fig.  244B)  are  dirty-white  creatures,  much 
wrinkled  in  appearance,  but  otherwise  quite  like  the  larvae  of 
houseflies.  The  tapering  anterior  end  of  the  body  is  provided 
with  a  pair  of  black  hooks  to  aid  in  piercing  the  skin  of  the  host, 
and  has  retractile  sucking  mouthparts.  The  thick  leathery  skin 
and  the  position  in  a  crack  in  the  ground  protects  the  larva  from 
injury  when  stepped  on  by  the  bare  feet  of  the  natives.  The 
body  is  beset  with  rings  of  spines  which  aid  in  the  wriggling 
method  of  locomotion.  The  maggots  are  inactive  in  the  day- 
time, but  come  forth  at  night  to  suck  the  blood  of  sleepers,  biting 
.  them  usually  on  the  side  of  the  body  next  to  the  ground.  The 
bites  are  less  irritating  than  those  of  mosquitoes,  and  according 
to  Roubaud  the  bites  of  20  larvae  at  once  produced  no  inflam- 
mation or  itching. 

Under  ideal  conditions  the  larvae  pass  through  two  moults  and 
go  into  the  pupal  stage  in  15  days,  but  this  may  be  extended  to 
about  two  and  one-half  months  under  unfavorable  conditions, 
such  as  low  temperature  and  irregular  food  supply.  The  pupal 
stage  lasts  about  11  days.  The  adults  do  not  begin  laying  eggs 
until  about  two  weeks  after  emergence.  The  whole  life  cycle, 
therefore,  from  egg  to  egg,  is  about  one  and  one-half  months 
under  favorable  conditions. 

The  Congo  floor  maggot  is  not  known  to  attack  any  animals 
but  man  in  nature,  though  a  closely  allied  maggot,  Chceromyia, 
lives  in  the  burrows  of  the  wart  hog  and  other  hairless  mam- 


CUTANEOUS  MYIASIS  513 

mals.     Its  bite  is  more  painful  to  man  than  is  that  of  the  normal 
human  parasite. 

The  attacks  of  the  floor  maggot  can  very  easily  be  avoided  by 
sleeping  on  mats  or  beds  raised  just  a  few  inches  from  the  ground. 

Maggots  Under  the  Skin 

There  are  several  species  of  flies  in  which  the  larvae  develop 
under  the  human  skin,  like  "  warbles  "  in  cattle,  but  they  are 
found  only  in  Africa  and  in  tropical  America.  The  African 
species  are  closely  related  to  the  blowflies  and  fleshflies,  whereas 
the  American  species,  of  which  there  is  usually  believed  to  be 
but  a  single  one,  is  a  true  botfly,  closely  allied  to  the  ox  warble. 


Fig.  245.     Adult  of   South   American   skin  maggot,  Dsrmatohia  hominis.      X  2. 
(After  Castellani  and  Chalmers.) 

Dermatobia,  —  The  American  species,  sometimes  called  the 
human  botfly,  Dermatobia  hominis  (Fig.  245),  is  found  through- 
out tropical  America  from  Mexico  to  northern  Argentina.  Its 
larvae  develop  not  only  in  man  but  also  in  many  other  animals, 
as  dogs,  cattle,  mules,  hogs,  etc.  In  certain  parts  of  South 
America  the  hides  of  cattle  become  so  riddled  with  the  perfora- 
tions made  by  these  bots  that  they  are  rendered  quite  worthless. 
The  infestation  in  man  is  contracted  chiefly  in  forest  regions,  and 
apparently  very  seldom  in  houses,  a  fact  which  possibly  accounts 
for  the  greater  degree  to  which  dogs  are  parasitized  by  it  than  are 
cats,  and  men  than  women  or  young  children. 

The  adult  fly  (Fig.  245)  is  about  the  size  of  a  blowfly  (half  an 
inch  in  length)  with  face  and  legs  yellowish,  thorax  bluish  black 
with  a  grayish  bloom,  and  the  abdomen  a  beautiful  metallic 


514 


FLY  MAGGOTS  AND  MYIASIS 


jt^hu.^ 


violet  blue.  The  mouthparts  are  not  fitted  for  piercing  flesh, 
and  there  is  no  **  stinger  "  at  the  posterior  end  of  the  body  to 
drill  a  hole  for  depositing  the  eggs.  Evidently,  therefore,  the 
many  accounts  which  one  can  find  of  the  fly's  biting  or  sting- 
ing at  the  time  the  eggs  are  deposited  are  faulty. 

The  manner  in  which  the  larvae  gain  access  to  the  skin  of  their 
hosts  is  one  of  the  most  remarkable  and  unusual  adaptations 
known  in  nature.  When  ready  to  oviposit,  the  female  fly  captures 
various  species  of  insects,  among  them  large  mosquitoes,  par- 
ticularly Janthinosoma  lutzi  (see  pp.  451-453),  various  flies  of  the 

family  Muscidse  including  the 
house  fly  and  stable  fly,  tabanids, 
and  possibly  ticks,  and  glues  her 
eggs  by  means  of  an  adhesive, 
quick-drying  cement  to  the  un- 
der side  of  the  abdomen  of  these 
insects.  When  the  latter  insects 
alight  upon  the  skin  of  warm- 
blooded animals  the  maggots 
emerge,  penetrate  the  skin  of 
the  host,  several  minutes  to  an 
hour  being  required  for  this 
process,  and  begin  their  de- 
velopment. According  to  Neiva 
and  Gomes,  captive  females  laid 
from  16  to  54  eggs  on  individual 

Fig.  246.  South  American  skin  mag-  flj^  ^^^  ^^^  Specimens  laid  a 
got,     Dermatooia    homims;    A,    dorsal  '  ^ 

view,   extended;   B,  ventral  view.      X  total    of   nearly   400    eggS.      EggS 

about  3.    (After  Neiva.)  frequently  found   on  leaves  are 

said  to  be  deposited  there  by  females  that  have  not  succeeded  in 
holding  flies  they  have  tried  to  capture,  and  are  compelled  to 
oviposit.  It  is  possible  that  the  flies  may  also  deposit  their  eggs 
directly  in  the  skin  of  the  host.  The  eggs  require  about  six  days' 
incubation,  after  which  the  larvae  are  ready  to  emerge  when  a 
suitable  occasion  is  presented.  The  larvae  may  partially  emerge 
from  the  egg  shells  and  then  draw  back  again  if  they  do  not  suc- 
ceed in  reaching  the  warm  skin  of  a  host. 

The  time  required  for  the  larvae  to  reach  maturity  in  the  host's 
skin  varies  from  five  to  ten  weeks.  They  ultimately  reach  a 
length  of  half  or  three-quarters  of  an  inch  (Fig.  246).  •  The  an- 
terior end  of  the  larva  is  broad  and  is  provided  with  double  rows 


CUTANEOUS  BOTS  515 

of  thorn-shaped  spines;  the  posterior  end  is  constricted,  espe- 
cially in  fully-developed  larvae,  and  does  not  possess  spines.  As 
the  larva  develops,  a  sort  of  boil  or  cyst  forms  about  it,  opening 
to  the  surface  of  the  skin  by  a  little  pore.  This  is  plugged  by  the 
posterior  end  of  the  maggot,  and  used  for  obtaining  air.  At 
intervals  these  warble-like  boils  give  rise  to  the  most  excruciating 
pain,  due,  no  doubt,  to  a  turning  over  or  moving  about  of  the 
spiny  larva  in  its  close  quarters.  When  mature  the  larvae  volun- 
tarily leave  their  host  and  fall  to  the  ground  to  pupate.  They 
transform  into  the  adult  form  in  the  course  of  several  weeks. 

The  swellings  under  the  skin  occupied  by  human  botflies,  as 
remarked  before,  are  very  painful  at  intervals,  while  at  other 
times  they  are  entirely  painless.  As  the  larva  matures,  a  puslike 
material  exudes  from  the  open  end  of  the  "  boil,"  containing, 
no  doubt,  the  excretions  of  the  maggot.  After  the  worm  has 
evacuated  its  cyst  or  has  been  removed  the  wounds  sometimes 
become  infected,  and  may  even  result  in  blood  poisoning  and 
death. 

The  method  usually  employed  to  remove  the  maggots  is  to 
apply  tobacco  juice  or  tobacco  ashes  to  the  infested  spots,  thus 
killing  the  worms  and  making  their  extraction  easy.  Another 
method  used  by  natives  in  some  parts  of  South  America  is  to  tie 
a  piece  of  fat  tightly  over  the  entrance  to  the  boil.  The  larva, 
deprived  of  air,  works  its  way  out  into  the  fat,  being  thus  induced 
to  extract  itself.  A  much  more  satisfactory  method  of  dealing 
with  the  worms  is  to  kill  them  with  an  injection  of  weak  carbolic 
acid,  mercuric  bichloride,  or  some  other  poisonous  substance, 
then  enlarge  the  entrance  to  the  cyst  with  a  sharp  clean  knife 
and  remove  the  body  of  the  worm.  A  washing  of  the  wound 
with  a  weak  carbolic  or  lysol  solution,  followed  by  an  antiseptic 
dressing,  obviates  any  danger  of  subsequent  infection.  The 
wound  heals  quickly  but  leaves  a  scar. 

Other  Bets.  —  Other  botflies  occasionally  infest  man  and  cause 
cutaneous  myiasis.  The  common  warble-flies  of  cattle.  Hypo- 
derma  lineata  and  H.  bovis  (Fig.  247),  have  been  recorded  as  oc- 
curring in  the  skin  or  flesh  of  human  beings  and  there  is  one  fatal 
case  on  record  where  an  ox  warble  caused  an  ulceration  in  the 
back  part  of  the  lower  jaw  of  a  boy  six  years  old.  Ox  warbles 
usually  gain  access  to  the  tissue  under  the  skin  of  cattle  in  an  in- 
direct way,  the  hairy  bee-like  flies  depositing  their  eggs  on  hairs 
of  cattle  where  they  will  be  licked  off.     As  soon  as  licked  the 


516  FLY  MAGGOTS  AND  MYIASIS 

eggs  hatch,  and  the  larvie  burrow  out  through  the  wall  of  the 
oesophagus,  migrate  through  whatever  tissues  they  may  find  in 
their  path,  and  ultimately  reach  a  position  just  under  the  skin, 
usually  on  the  back,  where  they  finish  their  development.  Occa- 
sionally the  larvae  penetrate  the  skin  directly,  but  the  indirect 


Fig.  247.     Larva  of  Hypoderma  hovis;    A,  posterior  view;    B,  lateral 
view.      X  2. 

method  is  the  usual  one.  Recent  investigations  indicate  that  the 
two  species  differ  somewhat  in  this  respect.  In  Russia  the  horse 
botfly,  Gastrophilus  hcemorrhoidalis,  which  normally  develops 
in  the  stomach  of  the  horse,  occasionally  lives  under  the  human 
skin. 

African  Skin  Maggots.  —  The  commonest  species  of  maggot 
which  develops  in  the  human  skin  in  Africa  is  the  '*  ver  du  Cay  or," 

the  larva  of  the  tumbu  fly, 
Cordylohia  anthropophaga. 
This  fly  belongs  to  the  same 
family  as  blowflies  and 
houseflies.  It  is  widespread 
throughout  Africa,  from 
Senegal  and  Khartoum  to 
the  Transvaal.  To  quote 
from  Fuller,  ''  There  is  no 
ill  the  flesh  is  heir  to  among 

Fig.  248.  Adult  female  of  African  skin  the  vicissitudeS  of  life  in 
maggoty  Cordylohia  anthropophaga.  X  3.  g^^^j^  Africa,  which  is  more 
(After  Castellan!  and  Chalmers.)  nc        • 

offensive  than  parasitism 
by  (this  insect)."  Man  is  not  the  main  host  of  the  larvae  of  this 
fly,  but  he  suffers  in  common  with  a  large  number  of  wild  and 
domesticated  animals,  especially  domestic  dogs. 

The  adult  fly  (Fig.  248)  is  about  the  size  of  a  blowfly  (half  an 
inch  long),  and  is  brown  in  color.  The  thorax  is  rusty  to  yellow- 
ish brown  with  indistinct  dusky  stripes,  the  abdomen  pale  brown, 
a  little  darker  toward  its  tip,  and  with  two  dusky  bands.     Ex- 


AFRICAN  SKIN   MAGGOT 


517 


actly  where  the  fly  deposits  its  eggs  or  newly  hatched  maggots  is 
not  quite  certain.  According  to  some  observations  the  living 
larvae  are  deposited  directly  on  the  skin  and  immediately  bore 
their  way  in,  while  according  to  others  the  eggs  or  young  larvae 
are  laid  on  the  hair,  on  clothing  which  has  been  hung  out,  on 
soiled  bed-clothes  of  children,  etc.  There  is  good  reason  to 
beUeve  that  the  fly  when  about  to  lay  eggs  is  attracted  by  fresh 
animal  smells,  such  as  perspiration,  fresh  excrement,  etc.,  when 
these  occur  on  the  skin  or  on  fabrics.  The  heads  of  infants, 
especially  if  not  kept  perfectly  clean,  are  favorite  places  for  the 
flies  to  deposit  their  offspring,  and  cases  are  on 
record  in  which  20  or  30  maggots  were  taken 
from  the  scalp  of  a  child  under  six  months  old. 
Woolen  clothing,  if  smelling  of  perspiration, 
is  almost  sure  to  become  infested  with  the 
maggots  when  hung  out  in  an  exposed  place, 
and  it  is  dangerous  to  put  on  such  clothing 
where  the  fly  is  abundant.  Roubaud,  in  ex- 
periments with  this  fly,  induced  a  specimen  to 
lay  150  eggs  on  the  walls  of  a  glass  vessel  and 
on  rotten  fruit,  and  obtained  infestation  of  a 
guinea-pig  with  15  larvae  hatched  apart  from 
the  host.  That  in  some  cases,  at  least,  the  eggs 
hatch  before  being  deposited  is  evident  from 
the  fact  that  living  maggots  can  sometimes  be 
squeezed  out  of  the  bodies  of  the  flies,  and  it  is  J^'l,l^l;,,^^^i'^^_ 
quite  probable  that  the  fly  normally  produces  loMa  anthropophaga, 
living  young.  The  maggots  are  usually  most  ^«J^^[  Bmmpt.)^  ^' 
abundant  in  the  southern  summer  (January  to 
March),  especially  in  March.  It  is  probable  that  there  are  not 
more  than  two  or  three  generations  a  year,  all  of  them  during  the 
summer,  the  rest  of  the  year  being  spent  in  the  adult  stage. 

The  maggots  (Fig.  249)  are  said  to  bore  into  the  skin  rapidly 
with  active  flapping  movements  and  without  causing  any  pain. 
As  pointed  out  by  Fuller  it  would  endanger  the  life  of  the  species 
if  in  entering  the  skin  it  excited  its  victim  to  dislodge  it.  Even 
if,  as  is  probably  often  the  case,  the  larva  enters  the  skin  during 
sleep,  unless  quite  painless  the  host  would  probably  wake  and 
scratch  it  out,  especially  in  the  case  of  wild  animals  which  must 
always  sleep  with  an  ear  and  an  eye  open,  so  to  speak.     As  many 


518  FLY   MAGGOTS  AND  MYIASIS 

as  300  maggots  have  been  taken  from  the  skin  of  a  puppy,  and 
it  is  not  unusual  for  20  or  more  to  be  present  at  once  in  a  human 
being.  They  come  to  rest  just  under  the  surface  of  the  skin, 
where  they  give  ris^  in  a  few  days  to  an  inflamed  boil,  the  in- 
flammation being  due  to  the  movements  of  the  spiny  worm,  and 
to  the  presence  of  toxic  excretions.  As  in  the  case  of  Dermatohia, 
an  opening  is  left  to  the  surface  of  the  skin  from  which  the  larva 
obtains  air  through  the  spiracles  at  the  posterior  end  of  the  body. 
In  some  cases  very  little  discomfort  is  felt  from  the  maggots, 
but  in  other  cases  an  intense  pain  is  caused  at  intervals. 

The  larva  is  a  fat,  creamy-white  maggot  which  reaches  a 
length  of  half  an  inch  when  full  grown.  It  is  bluntly  pointed 
at  the  anterior  end  but  broad  at  the  posterior  end.  The  body 
is  thickly  covered  with  minute  dark  brown  spines,  each  one  re- 
curved like  a  rose  thorn. 

Maturity  is  reached  in  about  two  weeks  or  less  from  the  time 
the  infestation  occurs,  though  usually  the  time  is  underestimated, 
due  to  the  fact  that  the  larva  is  not  noticed  during  the  early  part 
of  its  existence  in  the  skin.  When  fully  developed  the  larva 
voluntarily  leaves  its  host  and  falls  to  the  ground  to  pupate. 
The  pupa  is  of  the  usual  barrel-shaped  form  characteristic  of 
the  group  of  flies  to  which  this  species  belongs.  It  is  a  little 
less  than  half  an  inch  in  length,  at  first  of  a  light  rusty  color, 
later  turning  dark  purplish  brown.  The  adult  insect  emerges 
from  the  pupal  case  in  about  two  weeks. 

Preventive  measures  against  the  fly  consist  to  some  extent  in 
personal  cleanliness,  since  it  is  doubtful  if  the  flies  will  deposit 
their  offspring  except  on  surfaces  smelling  of  perspiration  or  other 
body  excretions.  Infants  seem  to  be  especially  subject  to  attack, 
and  should,  therefore,  be  kept  scrupulously  clean.  Since  the 
larva  of  the  fly  lives  readily  in  many  domestic  and  wild  animals, 
its  extermination  is  hardly  possible.  In  some  parts  of  Africa, 
notably  in  Natal,  the  worm  becomes  abundant  for  several 
seasons,  and  then  disappears  for  a  number  of  years.  The  reason 
for  this  is  not  understood. 

A  closely  allied  fly,  C.  rodhaini,  occurs  in  the  damp  equatorial 
forests  of  Africa,  attacking  thin-skinned  animals  such  as  an- 
telopes and  rodents,  and  occasionally  man.  Dogs,  cattle  and 
other  thick-skinned  animals  are  immune.  The  female  of  this 
species  may  deposit  over  500  eggs,  which  hatch  an  from  two  to 


SCREW- WORM  519 

four  days.  The  mature  larva,  which  closely  resembles  that  of 
C.  anthropophaga,  leaves  the  host  in  from  12  to  15  days,  buries 
itself  to  a  depth  of  several  inches  in  the  ground,  and  pupates. 
If  a  httle  moisture  is  present,  the  transformation  into  the  adult 
occurs  in  a  little  over  three  weeks.  About  two  months  is  required 
for  the  whole  life  cycle  of  this  fly. 


Myiasis  of  Wounds  and  of  Natural  Cavities  of  the  Body 

A  large  number  of  flies,  all  of  them  related  to  the  blowflies  and 
house;flies,  occasionally  deposit  their  eggs  or  newly  hatched 
larvae  in  neglected  wounds  when  offensive  discharges  are  exuding 
from  them.  In  severe  cases  infestations  with  maggots  of  these 
flies  may  lead  to  a  most  horrible  and  loathesome  death. 

The  instinct  of  the  female  flies  of  all  the  species  implicated  is 
to  deposit  offspring  in  places  from  which  the  odor  of  meat  or  of 
decaying  animal  matter  is  emanating,  regardless  of  where  the 
place  may  be.  This  instinct  is,  of  course,  of  the  highest  value 
to  the  species,  since  the  larvae  live  upon  the  substances  from  which 
such  smells  arise.  It  is  an  instinct  analogous  to  that  which 
causes  a  mosquito  to  lay  its  eggs  in  water,  or  a  horsefly  to  oviposit 
in  objects  overhanging  water  —  an  unknowing  but  accurate 
intuition  on  the  part  of  the  parent  to  provide  for  the  welfare  of 
its  young. 

Screw-worm.  —  One  of  the  most  important  species  in  this 
connection  is  the  American  screw-worm  fly,  Cochliomyia  (or 
Chrysomyia)  macellaria,  which  occurs  throughout  America  from 
Canada  to  Patagonia,  though  abundant  only  in  warm  countries. 

The  adult  fly  (Fig.  250A)  is  a  handsome  insect,  slightly  larger 
than  a  housefly,  of  a  metallic  blue-green  color  with  three  dark 
stripes  on  the  thorax.  It  belongs  to  the  family  Muscidae,  and 
to  the  same  section  as  the  ordinary  blowflies.  The  adults  con- 
gregate about  carcasses  of  dead  animals  on  which  they  ordinarily 
deposit  their  offspring  and  on  which  the  larvae  feed.  Records 
differ  as  to  whether  the  eggs  hatch  within  the  body  of  the  parent 
or  after  being  deposited,  and  it  is  probable  that  during  the  early 
part  of  the  season  and  in  cool  climates  the  eggs  are  deposited, 
while  under  other  circumstances  the  living  maggots  are  born. 
The  number  produced  by  a  single  fly  may  be  several  hundreds, 
but  they  are  deposited  with  amazing  rapidity.     The  maggots 


520 


FLY  MAGGOTS  AND  MYIASIS 


(Fig.  250B)  are  white,  footless  creatures,  provided  with  a  pair 
of  stout  hooks  near  the  mouth,  and  with  bands  of  minute  spines 
which  give  them  a  screwUke  appearance,  whence  they  derive 
their  name.  Eating  away  at  flesh  and  even  bone,  they  develop 
rapidly  to  a  length  of  about  half  an  inch,  and  maturity  may  be 

reached  in  three  days, 
though  four  or  five  days  is 
usually  required.  When 
fully  developed  the  larva 
leaves  its  feeding  grounds 
and  buries  itself  in  loose 
earth  nearby,  where  it 
pupates  in  two  or  three 
days.  The  pupae  are 
brown  in  color,  and  shaped 
somewhat  like  olives.  After 
four  days  or  more  in  the 
pupal  case  the  adult  insect 
emerges,  climbs  up  on 
nearby  herbage  and  rests  in 
a  characteristic  position 
with  the  head  down.     The 

Fig.  250.     Screw-worm  &y,  Cochliomyia  (or        .     ,       ■,.(.  ,       ^^„„^-   „ 

mrdlaria.    adult    and    maeeot.     whole     life      Cycle     OCCUpieS 


Chrysomyia)    macellaria,    adult    and    maggot 
X  3.     (Adult  after  Castellani  and  Chalmers,    from 
larva  after  Blanchard.) 


nine    days    to    two 
weeks  or  more. 

As  remarked  before,  the  female  screw-worm  fly,  about  to  re- 
produce, is  attracted  to  any  animal  smell  and  frequently  finds  a 
suitable  place  for  egg-laying  in  exposed  wounds,  or  in  the  nose  or 
ears  of  people  sleeping  out  doors,  especially  in  case  of  foul-smell- 
ing  catarrh.  Sometimes  the  flies  select  recently  vacated  Der- 
matohia  nests,  boils,  sores,  etc.,  for  the  young  to  develop  in.  As 
soon  as  hatched  the  maggots  begin  eating  their  way  into  the 
tissues  with  which  they  are  in  contact,  using  their  strong  man- 
dibles as  nippers  for  cutting  flesh  and  even  bone.  From  the 
ear  they  may  make  their  way  into  the  inner  ear,  completely  de- 
stroying the  auditory  apparatus.  From  the  nose  they  penetrate 
to  the  pharynx,  frontal  sinus,  the  eye-ball,  and  even  the  brain, 
occasionally  doing  such  extensive  damage  as  to  cause  death. 
Usually  an  abundant  discharge  of  pus  and  scraps  of  tissue,  in- 
tense pain,  and  delirium  accompany  the  infestation.     A  severe 


MYIASIS  OF  WOUNDS  521 

case  which  occurred  in  Kansas,  reported  by  Professor  Snow, 
was  substantially  as  follows:  The  victim  had  been  suffering 
from  nasal  catarrh  and  was  subject  to  offensive  discharges.  On 
August  22  he  complained  of  a  peculiar  sensation  at  the  base  of 
the  nose,  followed  by  violent  sneezing,  and  later  by  excruciating 
pain  in  the  region  of  the  forehead  back  of  the  nose.  On  the  24th 
there  was  a  profuse  discharge  of  offensive  matter  from  nose  and 
mouth  with  a  subsidence  of  pain,  the  discharge  continuing  three 
days  and  amounting  to  16  ounces,  becoming  almost  pure  pus  with 
particles  of  bone,  blood,  etc.,  in  it.  The  odor  was  very  offensive, 
and  coughing  and  fever  developed,  together  with  difficulty  in 
speech  and  swallowing.  At  this  time  a  maggot  dropped  from 
the  nose,  giving  the  first  inkling  of  what  the  trouble  was.  The 
worms  continued  to  drop  from  the  nostrils  and  mouth,  burrowing 
from  under  the  soft  palate  and  covering  of  the  hard  palate. 
The  palate  was  completely  honeycombed,  and  in  places  patches 
as  large  as  a  dime  were  entirely  destroyed.  The  estimated 
number  of  maggots  which  escaped  during  48  hours  was  over  300. 
The  whole  of  the  soft  palate  was  destroyed  by  this  time,  and 
the  patient  died  four  days  after  the  emergence  of  the  last  worm. 

Other  Species.  —  Although  the  screw-worm  is  the  species  most 
thoroughly  addicted  to  breeding  in  wounds  and  natural  cavities 
of  the  human  body,  it  is  by  no  means  alone  in  this  nefarious 
habit.  The  beautifully  colored  green-bottle  fly,  Lucilia  ccesar, 
and  other  species  of  Lucilia  have  this  habit,  and  the  common 
blowflies,  Calliphora  vomitoria  and  C.  erythrocephala,  are  sometimes 
implicated.  These  ubiquitous  pests  are  said  to  have  been  a 
great  torment  to  wounded  soldiers  in  the  Civil  War.  A  closely 
related  species  of  screw-worm,  Chrysomyia  hezziana,  widely  dis- 
tributed in  southern  Asia,  is,  according  to  Patton,  a  very  frequent 
parasite  of  man  and  animals  in  India.  From  observations  on 
habits  and  structure,  and  from  experimentation,  Patton  thinks 
this  species  deposits  its  eggs  only  in  living  animals.  Of  the  flesh- 
flies,  .which  are  related  to  the  Muscidae,  but  are  placed  in  a  separate 
family,  Sarcophagidae,  many,  and  possibly  all,  will  at  least  oc- 
casionally breed  in  wounds  or  natural  cavities  of  living  bodies. 

A  particularly  troublesome  species  in  Europe,  especially  in 
Russia,  where  it  is  almost  as  much  of  a  scourge  as  is  the  screw- 
worm  in  America,  is  the  fleshfly,  Wohlfartia  magnifica.  In  Rus- 
sia during  hot  weather  this  fly  attacks  the  nose,  ears,   mouth, 


522 


FLY  MAGGOTS  AND  MYIASIS 


sores,  wounds  of  any  kind,  or  even  the  eyes,  of  human  beings. 
In  one  case  70  maggots  were  extracted  from  one  eye  after  about 
this  many  had  already  escaped  and  been  thrown  away.  This 
fiy,  unhke  most  of  its  alHes,  is  said  to  attack  only  living  animals. 
The  larvae  are  unusually  resistant  to  substances  which  readily 
kill  other  insects;    they  will  survive  two  hours  in  95  per  cent 


Fig.  251.  Larva  of  fleshfly,  Sarcophaga;  A,  side  view  of  larva;  B,  posterior 
view  showing  posterior  spiracles  in  depression;  C,  anterior  spiracle,  marked  "sp." 
in  Fig.  A ;  D,  skeleton  of  pharynx,  with  mouth  hooks.    (After  Riley  and  Johannsen.) 

alcohol,  and  ten  minutes  in  turpentine  or  pure  hydrochloric  acid. 
This  species  is  said  to  be  a  great  pest  in  war,  where  it  causes 
myiasis  in  the  wounds  of  soldiers.  In  France  it  is  said  to  add 
much  to  the  sufferings  of  wounded  men. 

Other  fleshflies  occasionally  deposit  their  eggs  on  living  animals 
or  human  beings.  Sarcophaga  carnaria  is  particularly  likely  to 
deposit  eggs  or  larvae  in  the  vagina  when  it  has  access  to  it. 
As  in  the  case  of  the  flies  mentioned  above,  this  species  will 
readily  attack  the  nose  or  ears,  especially  if  there  is  a  foul-smell- 
ing catarrhal  discharge  flowing  from  it,  and  will  infest  inflamed 
or  diseased  eyes,  sometimes  nesting  in  large  numbers  under  the 
eyelids  and  eating  away  the  cornea. 

The  fleshflies  are  mainly  gray  in  color,  with  longitudinal  dark 
stripes  on  the  thorax  and  a  checkered  abdomen  which  is  change- 
able in  varying  lights.  In  summer  the  smell  of  decaying  flesh 
will  invariably  attract  them.  The  checkered  abdomen  and  the 
broad  angle  at  which  the  wings  are  held  serve  to  distinguish 
them  from  other  gray  flies.  Their  life  history  is  essentially  the 
same  as  that  of  the  screw-worm  fly. 

Another  fly  which  must  be  mentioned  in  this  connection  is 
the  sheep   head-maggot,  (Estrus  ovis,  a  species   of  botfly.     It 


INTESTINAL  MYIASIS  523 

normally  lays  its  eggs  in  the  nostrils  of  sheep,  from  which  place 
the  maggots  burrow  into  various  parts  of  the  head.  In  Algeria 
it  is  said  to  lay  its  eggs  while  flying  without  alighting,  upon 
the  eyes,  nostrils  and  lips  of*  shepherds,  especially  those  whose 
breath  smells  of  fresh  sheep  or  goat  cheese.  It  somewhat  re- 
sembles a  housefly,  but  is  larger  and  of  a  warmer  brown  color. 
Its  mouthparts  are  deficient  to  such  an  extent  that  the  fly  is 
incapable  of  feeding,  its  only  instincts  being  those  connected 
with  the  reproduction  of  its  kind. 

Treatment.  —  The  danger  arising  from  attacks  of  screw- 
worms  and  flies  of  similar  habits  is  that  the  infestation  is  often 
not  discovered  until  too  late.  Even  when  one  is  aware  of  an 
attack  by  the  fly,  it  is  not  always  possible  to  drive  it  away  soon 
enough  to  prevent  the  eggs  or  maggots  from  being  deposited. 
The  larvae  should  be  removed  as  speedily  as  possible  since  they 
may  do  a  great  deal  of  damage  in  a  very  short  time.  Usually 
the  maggots  may  be  induced  to  release  their  hold  and  to  fall 
out  by  douching  the  infested  part  of  the  body  with  a  20  per  cent 
solution  of  chloroform  in  sweet  milk,  or  with  a  carbolic  or  lysol 
wash.  Even  salt  water  is  often  effectiye  in  removing  the  mag- 
gots and  should  be  used  if  no  better  wash  is  at  hand.  Maggots 
in  the  ear,  if  outside  the  ear  drum,  should  be  removed  by  means 
of  water  or  milk  saturated  with  chloroform,  but  if  they  have 
already  pierced  the  ear  drum,  surgery  will  probably  be  necessary. 
Often  where  infections  are  two  or  three  days  old  surgery  must  be 
resorted  to  and  the  larvae  removed  by  means  of  curved  forceps. 
Frequent  antiseptic  washes  prevent  the  injuries  made  by  the 
maggots  from  becoming  infected  with  bacteria. 

Mjdasis  of  the  Intestine 

There  are  a  number  of  species  of  fly  maggots  which  may  ac- 
cidentally be  taken  into  the  intestine  of  man  and  cause  trouble 
there.  To  quote  from  Banks,  *'  When  we  consider  that  these 
dipterous  larvae  occur  in  decaying  fruits  and  vegetables  and  in 
fresh  and  cooked  meats;  that  the  blowfly,  for  example,  will 
deposit  on  meats  in  a  pantry;  that  other  maggots  occur  in  cheese, 
oleomargarine,  etc.,  and  that  pies  and  puddings  in  restaurants  are 
accessible  and  suitable  to  them,  it  can  readily  be  seen  that  a 
great  number  of  maggots  must  be  swallowed  by  persons  each  year, 


524 


FLY  MAGGOTS  AND  MYIASIS 


and  mostly  without  any  serious  consequences/'  Banks  gives  the 
following  quotation  from  Walsh,  —  "  Taking  everythmg  into  con- 
sideration, we  doubt  whether,  out  of  10,000  cases  where  the  larvae 
of  two- winged  flies  have  existed  in '  considerable  numbers  in  the 
human  intestines,  more  than  one  single  case  has  been  recorded 
in  print  by  competent  entomological  authority  for  the  edification 
of  the  world." 

Botflies.  —  There  are  some  flies  of  the  botfly  family,  CEstridoe, 
which  as  larvae  habitually  parasitize  the  digestive  tracts  of  horses 
and  other  domesticated  animals,  and  are  especially  adapted  in 
habits  and  structure  for  such  a  larval  life. 
They  occasionally,  though  rarely,  occur  in 
man.  The  horse  botfly,  Gastrophilus  equi, 
for  instance,  lays  its  eggs  (Fig.  252)  on  the 
hairs  of  horses  in  spots  where  they  are  likely 
to  be  licked.  The  moisture  and  rubbing 
of  the  horse's  tongue  cause  the  eggs  to 
hatch  at  once,  and  the  new  larvae,  adhering 
to  the  tongue,  make  their  way  to  the 
stomach  and  intestine  where  they  attach 
themselves  and  develop  to  full-grown  spiny 
larvae,  three-quarters  of  an  inch  in  length. 
In  the  following  spring  the  larvae  let  go  their 
hold,  pass  out  with  the  faeces  of  their  host 
and  pupate  in  the  ground.  Obviously  it 
could  be  only  by  a  ,  series  of  unusual  cir- 
cumstances that  these  larvae  could  gain  access 
(After  "to  the  human  stomach,  yet  a  number  of  cases 
have  been  recorded. 
Fannia  Larvae.  —  A  much  more  common  occurrence  in  man 
is  infection  of  the  intestine  with  larvae  of  various  species  of  house- 
frequenting  flies,  especially  the  lesser  housefly,  Fannia  canicu- 
larisj  and  the  latrine  fly,  F.  scalaris.  The  former  species  is  very 
common  in  houses  both  in  Europe  and  America.  It  closely 
resembles  the  housefly  but  is  smaller,  and  appears  earlier  in  the 
spring.  The  peculiar  manner  of  flight,  a  sudden  dart  followed  by 
a  hovering,  is  very  characteristic  and  a  good  means  of  identifica- 
tion. This  fly  is  frequently  observed  hovering  about  chandeliers 
hanging  near  the  center  of  rooms.  The  eggs  are  oval,  white 
objects  and  are  laid  in  decaying  vegetable  and  animal  matter 


Fig.  252.  Egg  of 
horse  botfly,  Gastro- 
philus equi,  attached 
to  hair;  gr.,  groove  for 
cementing  to  hair;  op., 
operculum. 
Collinge.) 


FANNIA  LARViE 


525 


and  sometimes  in  excrement.  The  occasional  presence  of  eggs 
in  partially  decayed  vegetables,  as  in  decayed  lettuce  leaves, 
rotten  fruit,  etc.,  probably  accounts  for  the  not  uncommon  ap- 
pearance of  the  larvae  in  the  human  intestine,  although  the  eggs 
may  also  be  laid  in  or  near  the  anus  of  people  using  unsanitary 
privies,  whence  the  larvae  work  their  way  up  into  the  large  in- 
testine. The  larvae  (Fig.  253)  are  very  different  from  those  of 
houseflies  and  blowflies,  being  broad  and  flattened,  about  one- 


-^^ 

-113x 

jlJ^ 

?.• 

1  " 

vJ 

»J 

7\ 

mdJL 

..J 

Fig.  253.     Larvae  of  Fannia  scalaris  (left)  and  Fannia  canicularia  (right).      X  8. 

(After  Hewitt.) 


fourth  of  an  inch  in  length  when  full  grown,  brown  in  color, 
with  rows  of  spiny  processes  to  which  adhere  particles  of  dirt 
and  filth.  The  latrine  fly,  F.  scalaris,  is  very  similar  to  the 
species  described  above,  but  is  larger  and  differs  in  minor  details 
of  form  and  habits.  It  prefers  excrement,  especially  himian 
excrement,  on  which  to  deposit  its  eggs,  and  has  gained  its  com- 
mon name  from  its  frequent  presence  about  privies  and  latrines. 
The  author  has  found  larvae  of  this  species  very  abundant  in 
chicken  manure.     The  adult  has  the  same  darting  and  hovering 


526  FLY  MAGGOTS  AND  MYIASIS 

manner  of  flight  as  its  close  relative,  F.  canicularis.  The  larvae 
(Fig.  253)  differ  from  those  of  the  latter  species  in  the  form  and 
arrangement  of  spines.  Several  cases  are  on  record  in  which 
Fannia  larvae  were  passed  in  the  faeces  intermittently  for  a  num- 
ber of  years,  often  accompanied  by  a  chronic  disorder  of  the 
intestine.  It  is  probable  in  these  cases  that  repeated  reinfections 
occur,  though  it  may  be  conceived  that  the  complete  life  history 
of  the  fly  could  be  passed  within  the  intestine  of  the  host.  The 
probability  of  this  seems  rather  remote. 

Other  Species.  —  Another  common  cause  of  intestinal  myiasis 
is  the  larvae  of  the  cheesefly,  Piophila  casei,  popularly  called 
"  cheese-skippers "  (Fig.  254).  These 
larvae  often  occur  in  abundance  in  old 
cheese,  and  also  in  ham,  bacon  and  other 
foods.  It  is  thought  by  some  people  that 
their  presence  in  cheese  is  an  indication 
of  particularly  good  cheese!  These  mag- 
gots resemble  diminutive  housefly  larvae, 
but  have  two  mouth  hooks  like  the  blow- 
fly maggots,  whereas  the  housefly  larvae 
have  a  single  median  one.  Probably  in 
Fig.  254.  Cheese-skipper  j^g^^y    cases    the    cheese-skippers    pass 

and   adult,   Piophila   casei.      ,  ,      ,       .  .  .  ,  ,    .  , 

X  3.  (After  Graham-  through  the  mtestme  without  domg  much 
Smith    from    Riley    and  damage,  but  they  sometimes  attack  the 

Johannsen.)  ^  •        i  i       t 

mucous  membranes,  causmg  bleedmg  sores 
which  may  become  infected  and  ultimately  lead  to  ulceration. 
Severe  pain  in  the  abdomen,  headache  and  vertigo  have  been 
known  to  be  caused  by  these  larvae  in  the  intestine. 

There  is  one  case  on  record  of  the  infection  of  a  Chinaman 
with  the  fleshfly,  Sarcophaga  fuscicauda.  He  passed  about  50 
larvae  in  each  stool  for  eight  days.  Occasional  infection  of  the 
intestine  with  maggots  of  other  species  of  flies  has  been  recorded, 
but  the  instances  are  so  rare  as  to  be  of  interest  only  as  ab- 
normal occurrences. 

The  powerful  resistance  of  fly  maggots  to  substances  which 
would  quickly  destroy  other  animals  makes  it  possible  for  many 
species  to  pass  through  the  stomach  safely  if  accidentally  swal- 
lowed either  as  eggs  or  young  worms.  As  said  before  experi- 
ments show  that  the  larvae  of  the  fleshfly,  Wohlfartia  magnificat 
can  survive  two  hours  in  95  per  cent  alcohol,  and  ten  minutes  in 


EFFECTS  OF  INTESTINAL  MYIASIS  527 

pure  hydrochloric  acid  or  turpentine.  It  is  a  little  wonder,  then, 
that  fly  maggots  are  not  destroyed  by  the  0.2  per  cent  hydro- 
chloric acid  of  the  stomach  or  by  the  other  digestive  juices. 

Effects.  —  The  effects  of  fly  larvae  in  the  intestine  are  extremely 
variable,  depending  on  the  heaviness  of  the  infection,  the  species 
of  flies,  and  on  individual  susceptibility.  There  are  many  cases 
where  the  presence  of  the  larvae  in  freshly  passed  stools  is  the 
first  indication  of  their  having  existed  in  the  intestine,  and  it  is 
practically  certain  that  the  majority  of  infections  are  never  known 
or  suspected. 

On  the  other  hand  more  or  less  serious  symptoms  may  be 
caused  by  intestinal  myiasis.  The  presence  of  Fannia  larvae  or 
of  cheese-skippers  in  the  digestive  tract  often  gives  rise  to  tem- 
porary intestinal  disturbances,  such  as  loss  of  appetite,  vomit- 
ing, general  malaise,  abdominal  pains,  diarrhea,  constipation  and 
intestinal  bleeding.  Sometimes  headache  and  vertigo  indicate 
the  absorption  of  toxic  substances  secreted  by  the  maggots  or 
their  entrance  to  the  blood  circulation  through  the  wounds. 
Four  cases  of  death  from  intestinal  myiasis  have  been  recorded, 
and  it  is  probable  that  appendicitis  may  sometimes  be  caused 
through  injury  to  the  walls  of  the  appendix  by  fly  larvae  which 
start  sores  leading  to  ulceration.  Those  maggots  which  pass 
directly  through  the  digestive  tract,  feeding  only  on  food  sub- 
stances with  which  they  come  in  contact  en  route,  do  little  or 
no  harm  to  the  temporary  host.  Those  larvae,  however,  which 
attack  the  living  tissues  lining  the  stomach  and  intestine  are  the 
cause  of  the  symptoms  named  above.  Even  the  maggots  of 
the  housefly,  Musca  domestica,  have  been  known  to  damage  the 
walls  of  the  digestive  tract.  In  a  case  which  occurred  in  the 
Philippines,  the  walls  of  the  stomach  were  extensively  eaten  away 
by  larvae  of  this  common  fly,  and  20  or  30  maggots  were  obtained 
by  means  of  a  stomach  pump.  A  liver  abscess  which  was  not  due 
to  the  usual  amebic  infection  accompanied  this  case,  but  whether 
due  directly  or  indirectly  to  the  myiasis  can  only  be  conjectured. 

Fly  maggots  can  usually  be  expelled  readily  by  means  of 
purges  and  doses  of  the  drugs  which  are  used  for  intestinal  worms 
(see  p.  237).  The  chief  danger  from  infection,  as  in  other  forms 
of  myiasis,  lies  in  the  fact  that  the  presence  of  the  maggots  is 
usually  not  even  suspected  until  much  of  their  damage  has  been 
done.     Prevention,  of  course,  consists  principally  in  care  as  to 


528  FLY  MAGGOTS  AND  MYIASIS 

what  is  eaten,  especially  in  regard  to  such  foods  as  raw  vegetables  * 
and  partly  decayed  fruits. 

Myiasis  of  Urinary  Passages.  —  Myiasis  of  the  urinary  pas- 
sages, both  urethra  and  bladder,  is  a  rare  but  occasional  occur- 
rence. The  flies  implicated  are  usually  the  lesser  housefly,  Fannia 
camcularis,  and  the  closely  alUed  latrine  fly,  F.  scalaris,  which 
have  already  been  described  in  connection  with  intestinal  myiasis. 
In  most  cases  infection  occurs  from  eggs  laid  near  the  external 
opening  of  the  urethra,  the  larvae  working  their  way  up  into  this 
tube  and  even  into  the  bladder;  apparently  they  need  very  httle 
oxygen.  Contamination  is  favored  by  sleeping  without  covers 
in  hot  weather,  so  that  flies  have  free  access  to  the  anal  and 
genital  region.  The  larvae,  when  escaping,  are  said  to  be  able  to 
project  themselves  with  a  flicking  motion  to  a  distance  of  from 
12  to  20  inches. 


SOURCES  OF  INFORMATION 

The  following  list  of  "  sources  of  information  "  includes  only 
those  periodicals  which  are  at  least  partly  devoted  to  parasitology 
and  preventive  medicine,  or  which  frequently  contain  important 
articles  on  these  subjects,  and  those  books  which  cover  the  entire 
subject  or  parts  of  it  in  a  comprehensive  manner.  Books  which 
are  out  of  date  and  have  been  superceded  by  newer  ones  are  not 
included.  Most  of  the  books  listed  contain  more  or  less  extensive 
bibliographies  which  should  be  of  great  assistance  to  anyone  who 
desires  to  pursue  any  phase  of  the  subject  of  human  parasitology 
beyond  the  hallway  to  which  this  book  may  lead  him. 

PERIODICALS 

United  States  and  Canada 

Amer.  Joum.  Publ.  Health,  New  York,  1911- 

Amer.  Journ.  Trop.   Diseases  and  Prev.   Med.,  New  Orleans,   1913-1915. 
(Merged  with  New  Orleans  Med.  and  Surg.  Joum.). 

Amer.  Joum.  Trop.  Med.,  Baltimore,  1921- 

Exper.  Sta.  Bull.  (Contains  synopsis  of  interest  in  sections  on  "  Economic 
Zoology  and  Entomology  "  and  "Veterinary  Medicine.") 

Harvard  School  Trop.  Med.,  Rep.  (one  issued),  1913- 

Index  Medicus,  Washington,  1879- 

Journ.  Amer.  Med.  Assoc,  Chicago,  1883-    (Contains  references  to  aU  current 
medical  literature,  and  reviews  of  much  of  it.) 

Journ.  Canad.  Med.  Assoc,  Toronto,  1911- 

Journ .  Cutaneous  Diseases,  Boston,  1 882-    (Continuation  of '  *  Journ .  Cutaneous 
and  Venereal  Diseases.") 

Journ.  Econ.  Ent.,  Concord,  1908- 

Journ.  Exper.  Med.,  New  York,  1896- 

Journ.  Inf.  Diseases,  Chicago. 

Journ.  Med.  Research,  Boston,  1901- 

Journ.  Parasitology,  Urbana,  1914- 

New  Orleans  Med.  and  Surg.  Journ.,  1844- 

Publ.  Internat.  Health  Comm.,  Rockefeller  Foundation,  New  York. 

Publ.  Rockefeller  San.  Comm.  for  Eradication  Hookworm  Disease.    Wash- 
ington. 

U.  S.  Bur.  Animal  Industry,  Bull.,  Washington. 

U.  S.  Bur.  Ent.,  Bull.,  Washington. 

U.  S.  Dep't>  Agr.,  Bull.,  Washington. 

U.  S.  Naval  Med.  Bull.,  Washington. 

U.  S.  War  Dep't  Bull.,  Washington. 

620 


530  SOURCES  OF  INFORMATION 

South  America 

Brazil  Medico,  Rio  de  Janiero,  Brazil,  1887- 

Cronica  Medica,  Lima,  Peru,  1884- 

Mem.  do  Inst.  Oswaldo  Cruz,  Maguinhos,  Rio  de  Janiero,  Brazil,  1909- 

Great  Britain 

Ann.  Trop.  Med.  and  Parasitology,  Liverpool,  1907- 

Brit.  Med.  Journ.,  London,  1857- 

Bull.  Entom.  Research,  London,  1910- 

Journ.  Econ.  Biology,  London,  1906- 

Journ.  Hyg.,  Cambridge,  1901- 

Jom-n.  London  School  Trop.  Med.,  London,  1911-1913 

Journ.  Royal  Army  Med.  Corps,  London,  1903- 

Journ.  Trop.  Med.  and  Hyg.,  London,  1898- 

Lancet,  London,  1823- 

Memoirs,  Liverpool  School  Trop.  Med. 

Parasitology,  Cambridge,  1908- 

Quarterly  Journ.  Micr.  Science,  London. 

Rep.  Sleeping  Sickness  Comm.  Roy.  Soc,  London,  1903- 

Review  Apphed  Entom.,  Ser.  B  (Med.  and  Vet.),  London,  1913- 

(Contains  reviews  of  all  important  work  on  medical    and  veterinary- 
entomology.) 

Sleeping  Sickness  Bull.,  London,  1908-1912 

Trans.  Soc.  Trop.  Med.  and  Hyg.,  London,  1907- 

Trop.  Diseases  Bull.,  London,  1913- 

(Contains  reviews  of  all  important  work  on  tropical  diseases,  including 
nearly  all  work  on  protozoan  parasites  and  on  helminthology.) 

France 

Ann.  d'hyg.  et  de  med.,  Paris,  1898- 

Ann.  de  I'institute  Pasteur,  Paris,  1887- 

Arch.  de  parasitologic,  Paris,  1898- 

Bull.  de  la  soc.  de  path,  exotique,  Paris,  1908- 

Bull.  Sci.  de  la  France  et  de  la  Belgique,  1888- 

Comp.-Rend.  de  la  soc.  de  biol.,  Paris,  1849- 

Comp.-Rend.  des  seances  de  I'acad.  des  sci.  Paris,  1835- 

Revue  de  med.  et  d'Hygidne  tropicales,  Paris,  1904- 

Germany  and  Austria 

Arch,  fiir  Protistenkunde,  Jena,  1902- 

Arch.  fiir  Schiffs-  und  Tropen-Hyg.,  Leipzig,  1897- 

Bibliographica  Zoologica. 

Centralblatt  fiir  Bakt.  und  Parasitologic,  1  abt.,  Orig.  und  Ref.,.Jena,  1887- 
(Ref .  contains  references  and  reviews  of  many  articles  dealing  with  in- 
fectious diseases.) 


PERIODICALS  531 

Deutsche  Med.  Wochenschrift,  Berlin,  1875- 
Wiener  Klinische  Wochenschrift,  Vienna,  1888- 
Zeitschr.  fiir  Hyg.  und  Infektionskrank.,  Leipzig,  1886- 

ItaLy 
Annali  d'Igiene,  Rome,  1895- 
Malaria  e  Malattie  dei  Paesi  Caldi,  Rome,  1910- 
Malariologia,  Rome,  1908- 
Policlinico,  Rome,  1893- 
Pediatria,  Naples,  1893- 

PortugcJ, 
Arch,  de  hyg.  e  path,  exot.,  Lisbon,  1905- 

Asia 

China  Med.  Journ.,  Shanghai,  1887-  (Contains  bimonthly,  beginning  1916, 
"Japanese  Medical  Literature,"  a  review  in  English  of  current  Japanese 
medical  work,  also  issued  separately.) 

Ind.  Journ.  Med.  Research,  Calcutta,  1913- 

Ind.  Med.  Gazette,  Calcutta. 

Philip.  Journ.  Sci.,  Ser.  B  (Trop.  Med.),  Manila,  1906- 

Proc.  All  India  San.  Conferences. 

Sci.  Mem.  by  Officers  Med.  and  San.  Dep't  of  Gov't  of  India,  Calcutta. 

Africa 

Arch,  de  I'inst.  Pasteur,  Tunis,  1906- 

Nyasaland  Sleeping  Sickness  Diary,  Zomba,  1908- 

Rep.  Wellcome  Research  Lab.,  Khartoum,  1906- 

Australia 
Australian  Inst.  Trop.  Med.,  Collected  Papers,  Townsville,  1914- 

BOOKS 

General 

Bolduan,  C.  F.,  and  Koopman,  J.  Immune  Sera,  5th  ed.,  206  pp.,  9  figs., 
New  York,  1917. 

Braun,  M.,  and  LtJHE,  M.  Handbook  of  Practical  Parasitology  (trans- 
lated from  German  by  L.  Forster),  vii  +  208  pp.,  ill.,  1910. 

Braun,  M.  Die  Tierischen  Parasiten  des  Menschen,  5th  ed.  Part  1,  Natur- 
geschichte,  560  pp.,  407  figs.,  Wurzburg,  1915.  Part  2  by  Siebert,  O.,  to 
appear  later. 

Breinl,  Anton.  The  Distribution  and  Spread  of  Disease  in  the  East; 
Protozoa  and  Disease;  The  Influence  of  Climate,  Disease  and  Sur- 
roundings on  the  White  Race  Living  in  the  Tropics  (Stewart  Lectures 
of  Univ.  of  Melbourne)  31  pp.,  Melbourne,  1914. 


532  SOURCES  OF  INFORMATION 

Brumpt,  E.     Precis  de  parasitologie,  xxviii  +  1011  pp.,  Paris,  1913. 
Castellani,  a.,  and  Chalmers,  A.  J.     A  Manual  of  Tropical  Medicine, 

3rd  ed.,  x  +  2436  pp.,  909  figs.  16  pis.,  London  and  New  York,  1919. 
Fantham,  H.  B.,  Stephens,  J.  W.  W.,  and  Theobald,  F.  V.     The  Animal 

Parasites  of  Man  (partly  adapted  from  Braim's  "Die  Tierischen  Para- 

siten  des  Menschen),  xxvii  +  900  pp.,  London,  1916. 
Hegner,  R.  W.,  and  Cort,  W.  W.     Diagnosis  of  Protozoa  and  Worms 

Parasitic  in  Man.     72  pp.,  8  pis.,  Baltimore,  1921. 
Laloy,  L.     Parasitisme  et  mutualisme  dans  la  nature,  284  pp.,  82  figs., 

Paris,  1906. 
Leuckart,  R.     Die  Parasiten  des  Menschen  und  die  von  ihnen  herruhrenden 

Krankheiten,  2nd  ed.,   (also  English  translation),  Leipzig  and  Heidel- 
berg, 1886-1889. 
M ANSON.     Tropical  Diseases,  ed.  by  Manson-Bahr,  P.  H.,  7th  ed.,  xvi  +  960 

pp.,  404  figs.,  27  pis.,  31  charts,  London  and  New  York,  1921. 
Mense.     Handbuch  der  Tropenkrankheiten,  Band  I,  1905. 
Neumann,  R.  O.,  and  Mayer,  M.     Atlas  und  Lehrbuch  wichtiger  tierischer 

Parasiten  und  ihrer  Uebertrager.     Vol.  IX  of  Lehman's  Medizinische 

Atlanten,  vi  +  580  pp.,  45  pis.,  237  figs.,  Munich,  1914. 
Neveu-Lemaire,  M.     Precis  de  parasitologie  humaine,    parasites  vegetaux 

et  animaux,  4th  ed.,  Paris,  1911. 
RiVAS,  D.     Human  Parasitology,  715  pp.,  422  figs.,  18  pis.,  Philadelphia,  1920. 
Shipley,  A.  E.     The  Minor  Horrors  of  War.  184  pp.,  London,  1915. 
Stitt,  E.  R.     Practical  Bacteriology,  Blood  Work  and  Animal  Parasitology, 

6th  ed.,  xi  +  633  pp.,  1  pi.  177  figs.,  Philadelphia,  1921. 
ZiNSSNER,  H.    Infection  and  Resistance,  xiii  +  546  pp.,  ill.,  New  York,  1914. 


Protozoology  and  Helminthology 

BoYCE,  R.     Yellow  Fever  and  Its  Prevention,  396  pp.,  London,  1911. 
Brahmachari,  U.     Kala-azar  and  Its  Treatment,  2nd  ed.,  vii  +  258  +  8  pp., 

16  pis.,  24  charts,  Calcutta,  1920. 
Bruto  da  Costa,  B.  F.,  Santa  Anna,  J.  F.,  dos  Santos,  A.  C,  and  de  Aranjo 

Alvares,   M.   G.     Sleeping  Sickness,   a  Record  of  Four  Years'   War 

Against  it  in  the  Island  of  Principe  (Trans,  from  Portuguese  by  WyHie, 

J.  A.),  xii  +  261  pp.,  ill.,  London,  1916. 
Calkins,  Gary  N.     Protozoology,  ix  +  349  pp.,  125  ill..  New  York,  1909, 
Clark,  J.  J.     Protozoa  and  Disease,  4  vols.,  London  and  New  York,  1903- 

1916. 
Craig,  C.  F.     The  Malarial  Fevers,  Hsemoglobinuric  Fever  and  the  Blood 

Protozoa  of  Man,  New  York,  1909. 
Dobell,  €.     The  Amcebae  Living  in  Man,  vii  +  155  pp.,  5  pis.  London,  1919. 
DoBELL,  C,  AND  O'CoNNOR,  F.  W.     The  Intestinal  Protozoa  of  Man,  ix  + 

211  pp.,  8  pi.,  2  figs.,  London,  1921. 
DoFLEiN,  F.     Lehrbuch  der  Protozoenkunde,  3rd  ed.,  xii  +  1043  pp.,  951 

figs.,  Jena,  1911. 
Fantham,  H.  B.,  and  Porter,  A.     Some  Minute  Animal  Parasites,  319  pp., 

56  figs.,  Jena,  1911. 


BOOKS  533 

Hazen,  H.  H.     Syphilis,  650  pp.,  160  figs.,  16  pis.,  St.  Louis,  1919. 

KoLLE,  W.,  AND  Wasserman,  E.  VON.  Handbuch  der  Pathogenen  Mikro- 
organismen,  2nd  ed.,  Band  VII  (Protozoa),  1039  pp.,  121  figs.,  20  pis., 
and  Band  VIII  (Worms  and  Obscure  Organisms),  1109  pp.,  372  figs.,  22 
pis.,  1913. 

Laveran,  a.,  and  Mesnil,  F.  Trypanosomes  et  Trypanosomiases  (1904  ed. 
trans,  to  English  by  D.  N.  Nabarro),  Paris  and  Chicago,  1912. 

Loess,  A.  The  Anatomy  and  Life  History  of  Ankylostoma  duodenale,  451 
pp.,  19  pis.,  Cairo,  1908. 

MacNeal,  W.  J.  Pathogenic  Micro-organisms,  xxi  +  462  pp.,  213  ill.,  Phila- 
delphia, 1914. 

MiNCHiN,  A.  E.  An  Introduction  to  the  Study  of  the  Protozoa,  xi  +  517 
pp.,  London,  1912. 

Phillips,  L.  P.     Amoebiasis  and  the  Dysenteries,  xi  +  147  pp.,  London,  1915. 

Prowazek,  S.  von.     Taschenbuch  der  Mikroscopischen  Technik  der  Protis- 
ten-untersuchungen,  Leipzig,  1909. 
Handbuch  der  Pathogenen  Protozoen,  in  6  Lief.,  in  all  878  pp.,  24  pis.,  310 
figs.,  Leipzig,  1912-1914. 

Ross,  R.     The  Prevention  of  Malaria,  xx  +  669  pp.,  London,  1910. 

STAiJBLi,  C.     Trichinosis,  Wiesbaden,  1909. 

Stephens,  J.  W.,  and  Christophers,  S.  R.  The  Practical  Study  of  Malaria 
and  Other  Blood  Parasites,  ix  +  414  +  xiv  pp.,  6  pis.,  ill.,  London,  1908. 

Thimm,  C.  a.  Bibliography  of  Trypanosomiasis.  Issued  under  the  Direc- 
tion of  the  Honorary  Managing  Committee  of  the  Sleeping  Sickness 
Bureau,  London,  1909. 

Medical  Entomology 

Alcock,  a.     Entomology  for  Medical  Offices,  2nd  ed.,  xv  +  380,  197  figs., 

London,  1920. 
Austen,  E.     African  Blood-sucking  Flies,  British  Mus.  Publ.,  London,  1909. 

A  handbook  of  the  Tsetse  Fhes,  British  Mus.  Publ.,  x  +  110  pp.,  24 

figs.,  10  pis.,  London,  1911. 
Boyce,  R.  W.     Mosquito  or  Man?     The  Conquest  of  the  Tropical  World, 

xvi  +  267  pp.,  44  pis.,  New  York,  1909. 
DoANE,  R.  W.     Insects  and  Disease,  xiv  +  227  pp..  New  York,  1910. 
Graham  Smith,  G.  S.     Flies  in  Relation  to  Disease  (Non-Blood-Sucking 

Flies),  xiv  +  292  pp.,  Cambridge,  1913. 
Hegh,  E.     Notice  sur  les  glossines  ou  testses,  148  pp.,  29  figs.,  London,  1915. 
Herms,  W.  B,     Medical  and  Veterinary  Entomology,  xii  +  393  pp.,  228  figs., 

New  York,  1915. 
HiNDLE,  E.     Flies  and  Disease  (Blood-Sucking  Fhes),  414  pp.,  ill.,  Cambridge, 

1914. 
Howard,  L.  O.,  Dyar,  L,  and  Knab,  F.     The  Mosquitoes  of  North  and 

Central  America  and  the  West  Indies,  Carnegie  Inst.  Publ.,  4  vols., 

520  +  1064  pp.,  14  +  150  pis.,  Washington,  1913-1917. 
Larrousse,   F.     fitude  Systematique  et  Medicale  des  Phl^botomes.     106 

pp.,  20  figs.,  Paris,  1921. 


534  SOURCES  OF  INFORMATION 

LePrince,  J.  A.,  AND  Orienstein,  a.  J.     Mosquito  Control  in  Panama,  with 

Introduction  by  L.  O.  Howard,  xvii  +  335  pp.,  100  ill.,  New  York,  1916. 
NuTTALL,  G.  H.  F.,  Warburton,  C,  Cooper,  W.  F.,  and  Robinson,  L.  E. 

Ticks;  a  Monograph  of  the  Ixodoidea,  Parts  1  to  3,  Cambridge,  1908-1915 
Patton,  W.  S.,  and  Cragg,  F.  W.     A  Textbook  of  Medical  Entomology, 

764  pp.,  London,  1913. 
Pierce,  W.  D.    Sanitary  Entomology,  xxvi  +  518  pp.,  88  figs.,  Boston,  1921. 
Riley,  W.  A.,  and  Johannsen,  O.  A.     A  Handbook  of  Medical  Entomology, 

ix  +  348  pp.,  174  figs.,  Ithaca,  1915. 
Russell,  H.     The  Flea,  125  pp.,  9  figs.,  Cambridge,  1913. 


INDEX 


Abyssinia,  relapsing  fever,  44;  tape- 
worm infections,  240;  Ornitho- 
dorus  savignyi,  361,  368,  369. 

Acanthaspis  sulci-pes,  and  endemic 
goitre  in  Africa,  382. 

Acanthocephala,  199;  283-285. 

Acanthocheilonema  perstans,  see  Fi- 
laria  perstans. 

Acarina,  324;  331-333;  see  also 
mites. 

Acid,  resistance  of  maggots  to,  522. 

Acne,  relation  of  Demodex  to,  347. 

Adaptations,  of  parasites  and  hosts, 
14-15. 

Aden,  phlebotomus  fever  outside 
range  of  Phlebotomus  papatasii, 
470. 

Aedes,  intermediate  host  of  Filaria 
bancrofti,  301. 
ccdopus,  and  yellow  fever,  70,  72, 
443;  443-448;  and  dengue, 
183,  448;  time  of  activity,  436, 
444;  food  preferences,  436; 
description,  443-444;  habits, 
444;  breeding,  444-447;  habits 
of  larv2e,  446;  flight  and  dis- 
tribution, 447-448. 
pseudoscutellaris,  intermediate  host 

of  Filaria,  301,  450. 
sollicitans,  migrations,  435. 
spenceri,  habits,  436. 

Africa,  relapsing  fever,  42,  43;  yaws,. 
63;  yellow  fever,  69;  spiro- 
chaetal  bronchitis,  73b;  kala- 
azar,  77;  importance  of  sleep- 
ing sickness,  93;  distribu- 
tion of  Trypanosoma  gambiense 
and  T.  rhodesiense,  98;  malaria, 
147-148;  blackwater  fever,  161; 
Schistosoma    hcemxitobium,    213, 


Schistosomxi  mnnsoni,  217; 
Gastrodiscoides  in  horses,  229; 
Watsonius  watsoni,  229;  Hyme- 
nolepis  nana,  242;  Taenia 
africana,  245;  Diphylloboth- 
rium  latus,  246;  Sparganum 
mansoni,  252;  Necator  ameri- 
canus,  255;  Physaloptera  mor- 
dens,  282;  Ternidens  deminutus, 
283;  (Esophagostomum  apio- 
stomum,  283;  CE.  stephano- 
stomum,  283;  Filaria  per  dans, 
307-308;  Loa  loa,  308,  489; 
Chrysops  with  larval  filariae,  310 
489;  Onchocerca  volvulus,  310; 
Dracunculus  medinensis,  311; 
aquatic  leeches,  317;  tick 
paralysis,  358-359;  Ornitho- 
dorus  moubata,  360;  Argas  re- 
flexus,  364;  Otiobius  meg' 
nini,  365;  Amblyomma  hebrcBum, 
367;  Cimex  hemipterus,  373; 
Triatomn  rubrofasciatus,  381; 
Acanthaspis  suldpes,  382;  Xenop- 
sylla,  417;  chigger,  419;  malaria- 
carrying  Anopheles,  441;  oil 
films  for  mosquito  larvae,  459; 
Phlebotomus  papatasii,  470,  471; 
tsetse  flies,  490,  492;  Glossina 
morsitans,  493,  499;  Glossina 
palpalis,  498;  other  species  of 
Glossina,  500-501 ;  destruction 
of  wild  game,  503-504;  blood- 
sucking maggots,  511-513;  skin 
maggots,  513,  516-519. 
African  relapsing  fever,  relation  of 
ticks  to,  8,  43-46;  importance, 
42;  transmission,  43-44,  360- 
361;  in  Persia,  44;  severity, 
47. 


535 


536 


INDEX 


African  skin  maggot,  see  Cordylobia 
anthropophaga. 

Agglutination,  21;  of  trypanosomes, 
102-103. 

Agramonte,  C.  a.,  70,  443. 

Akamushi,  see  Leptus  akamushi. 

Akashi,  244. 

Alcock,  a.,  433,  449,  478. 

Alcohol,  in  prevention  of  filarial  in- 
fection, 307;  for  red-bug  rash, 
336;  resistance  of  maggots  to, 
522,  526. 

Alcresta  ipecac,  for  Balantidium  in- 
fections, 127;  for  amebic  dys- 
entery, 138. 

Algeria,  relapsing  fever  transmission, 
44,  398;  infantile  kala-azar,  82; 
sheep     head-maggot,     522-523. 

Alum,  for  fleas,  421. 

Amblyomma,  366. 
cajennense,  367. 
hebrceum,  367. 

Amebse,  cultivation,  9;  encysted,  in 
Egypt,  34;  128-146b;  classifi- 
cation, 128-132;  and  dysentery, 
135-140;  effect  of  emetin  on, 
137-138;    of  mouth,   142-146b. 

Amebic  dysentery,  in  United  States, 
6;  135-140;  importance,  135; 
parasites  of,  135-136;  course  of, 
136-137;  carriers,  136;  treat- 
ment, 137-139;  prevention, 
139-140. 

America,  relapsing  fever,  42,  43; 
origin  of  syphilis,  48;  importa- 
tion of  yaws,  63;  yellow  fever, 
69-70,  72;  possibility  of  kala- 
azar,  77;  introduction  of 
sleeping  sickness,  93;  Schisto- 
soma mansoni,  217;  Hymeno- 
lepis  nana,  242;  introduction 
of  Necator  americanus,  255; 
hosts  of  trichina,  288;  Demodex 
'  folliculorum,  347;  Ambly- 
omma cajennense,  367;  original 
home  of  Aedes  calopus,  447; 
Culex  quinquefasdatus,  449; 
Janthinosoma     lutzi,     453;     oil 


of  citronella  as  repellent  for 
mosquitoes,  455;  Chironomidae, 
474;  skin  maggots,  513-516; 
screw- worm,  519;  Fannia,  524. 
See  also  various  geographic  sub- 
divisions. 

American  hookworm,  see  Necator 
americanus. 

American  HookAvorm  Commission, 
use  of  thymol,  263;  work  of,  268. 

American  leishmaniasis,  see  Es- 
pundia. 

American  Red  Cross,  work  in  Ser- 
bia, 378,  398;  work  on  trench 
fever,  187,  397,  399. 

American  Yellow  Fever  Commis- 
sion, 7-8,  70,  443. 

Ammonia,  for  red-bug  rash,  335; 
for  body  lice,  402. 

Amoeba,  131;  see  also  amebae. 

Anaphylatoxin,  23-25. 

Anaphylaxis,  23-25;  specific,  24; 
treatment,  25. 

Ancon,  manufacture  of  larvicide, 
459. 

Ancylostoma  duodenale,  distribution, 
255;   description,  255-257. 
ceylanicum,  255. 

Anderson,  J.  F.,  8,  397. 

Andes,  uta,  86;  Oroya  fever,  178, 
472;  Phlebotomus  verrucaru7n, 
473. 

Animal  experimentation,  10-11. 

Anise  oil,  for  bod}^  lice,  401;  for  mos- 
quitoes, 455;  for  phlebotomus 
flies,  473. 

Anisol,  for  body  lice,  401. 

AnneHda,  199-200;  215;  relation  to 
arthropods,  323;  see  also 
Leeches. 

Anopheles,  malaria-carrying  species, 
157-158,  438,  439-441;  and 
malaria  in  winter,  156;  cessa- 
tion of  breeding  and  sub- 
tropical malaria,  162;  number 
necessary  to  propagate  malaria, 
165;  intermediate  host  of 
Filaria     bancrofti,     301,     450; 


INDEX 


537 


palpi,  426;  eggs,  429;  larvae, 
431,  442;  time  of  activity, 
435,  437;  identification,  438- 
439;  habits,  441-443;  variable 
ability  of  species  to  transmit 
different  kinds  of  malaria,  439; 
effect  of  oil  on  larvae,  458;  effect 
of  larvicide,  459. 

alhimaniis,  and  malaria  in  tropical 
America,  439. 

argyrotarsus,  and  malaria  in  tropi- 
cal America,  441. 

bancrofti,  and  malaria  in  Australia, 
441. 

hifurcatus,  hibernation,  441. 

hraziliensis,  habits,  441. 

costalis,  and  malaria  in  Africa,  441. 

crucians,  relation  to  various  types 
of  malaria,  439. 

culicifacies,  and  malaria  in  India, 
441. 

cruzi,  habits,  442. 

eiseni,  habits,  441-442. 

funesta,  and  malaria  in  Africa,  441. 

listoni,  and  malaria  in  India,  441; 
in  China  and  Japan,  441. 

ludlowi,  and  malaria  in  East  In- 
dies, 441;  habits,  442. 

maculipennis,  and  malaria  in 
Europe,  441. 

malefactor,  not  a  malaria  carrier, 
158,  434. 

punctipennis,  development  of 
Ldshmania  donovani  in,  78; 
relation  to  certain  types  of  ma- 
laria, 439. 

quadrinmculatus,  resistance  of 
Plasmodium  vivax  to  low  tem- 
peratures in,  156;  carrier  of  cer- 
tain types  of  malaria,  439;  de- 
velopment, 442. 

sinensis,  and  malaria  in  China  and 
Japan,  441. 

stephensi,  and  malaria  in  India, 
441. 

umhrosus,  and  malaria  in  Malay 
countries,  441;  habits,  441. 

willmori,   and   malaria   in    Malay 


countries,  441;  habits,  441. 

Anoplura,  388;  see  also  lice. 

Antelope,  host  of  Tomia  saginata, 
240;  host  of  tsetse  flies,  490; 
host  of  Cordylobia  rodhaini,  518. 

Anthelmintics,  270. 

Anthrax,  and  tabanids,  488;  and 
stable-flies,  488,  507. 

Antibodies,  21;   duration,  22. 

Antigen,  22. 

Antimony,  metallic,  in  kala-azar,  81; 
compounds  in  trypanosomiasis, 
104-105;  see  also  Tartar  emetic. 

Antitoxin,  21. 

Anti-vivisectionists,  10-11. 

Apes,  hosts  of  Trypanosoma  cruzi, 
112;  relation  of  intestinal 
worms  to  typhoid  in,  204. 

Aphthomonas  infestans,  and  foot-and- 
mouth  disease,  76,  193. 

Aphthous  fever,  see  Foot-and-mouth 
disease. 

Aponomma,  366. 

Appendicitis,  relation  of  intestinal 
worms  to,  204;  and  intestinal 
myiasis,  527. 

Arabia,  oriental  sore,  85;  Ornitho- 
dorus  savignyi,  361;  tsetse  flies, 
492,  500. 

Arachnida,  324. 

Aradidse,  383. 

Aragao,  H.  deB.,  73d,  130. 

Archi-annelida,  199. 

Arctomys  bobac,  and  plague  in  Man- 
churia, 413. 

Argas  miniatv^,  see  A.  persicus. 
persicus,  and  relapsing  fever,  45, 
361;    importance,  364;    control, 
369. 
reflexu^,  364. 

Argasidae,  egg-laying  habits,  355; 
general  characteristics,  366- 
357;  important  species,  364- 
366. 

Argentina,  trypanosoi.-^o  .n  Tna- 
toma,  108,  112,  381;  dengue, 
182;  Tetranychus  molestissimus, 
341. 


538 


INDEX 


Armadillo,  host  of  Trypanosoma 
cruzi,  112;  and  Triatoma  genicu- 
lata,  380-381. 

Arsenic,  in  trypanosomiasis,  104-105; 
see  also  atoxyl  and  tryparsamide. 

Arsenical  dip,  to  remove  ticks  from 
domestic  animals,  368. 

Arsenobenzol,  for  guinea-worms,  314. 

Arthropoda,  322-330;  importance, 
322;  role  in  disseminating 
disease,  7-8,  322-323;  relation- 
ships, 323-324;  classification, 
324-325. 

Ascaris,  nutriment  absorbed,  202; 
toxins,  202-203;  273-276;  de- 
scription, 273;  life  history,  274- 
275;  symptoms,  276;  treatment 
276. 
lumbricoides,  274. 

marginata,  see  Toxascaris  limbata. 
mystax,  see  Belascaris  cati. 
suilla,  274. 

Ascaridae,  282. 

AsHBURN,  P.  M.,  301,  448. 

Asia,  oriental  sore,  84;  blackwater 
fever,  161;  dengue,  182;  keda- 
ni,  190;  Schistosoma  hoemato- 
hium,  213;  Clonorchis  sinensis, 
224;  Yokagawa  yokagawa,  228; 
Heterophyes  heterophyes,  228; 
Fasdolopsis  buski,  229;  Hyme- 
nolepis  nana,  242;  Necator  amer- 
icanus,  255;  Filaria  hancrofti, 
299;  Dracunculus  medinensis, 
311;  Porocephalus  moniliformis, 
351;  Cimex  hemipterus,  373; 
Triatoma  rubrofasciata,  381; 
Xenopsylla,  417;  Phlebotomus, 
470;  surra,  487;  Chrysomyia 
bezziana,  521. 

Asopia,  farinalis,  intermediate  host 
of   Hymenolepis    diminuta,  244. 

Assam,  eradication  of  kala-azar,  82. 

Astacus  japonicus,  intermediate  host 
of  lung  fluke  in  Korea,  222. 

Atkin,  E,  E.,  445,  446. 

Atoxyl,  discovery,  8;    for  trypano- 
somes,  105. 


Aucheromyia  luteola,  511-513;  de- 
scription, 511;  life  history,  511- 
512;  maggots,  512;  avoidance 
of,  513. 

Australia,  Aedes  calopus  carrier  of 
dengue,  448;  hydatids,  248, 
250;  Filaria  bancrofti,  299; 
land  leeches,  319-320;  tick  par- 
alysis, 358-359;  malaria-carry- 
ing Anopheles,  441;  Aedes 
calopus,  448;  transmission  of 
dengue,  448;  Pericoma  towns- 
villensis,  466. 

Austria,  relapsing  fever,  43;  typhus, 
398. 

Auto-salvarsanized  serum,  for  syph- 
ilis of  nervous  system,  57;  for 
sleeping  sickness,  106. 

Axopodia,  31. 

Axostyle,  32. 

Baboon,  host  of  Trichostronglyus  in- 
stabilis,  282;  fed  upon  by  tsetse 
flies,  500. 

Bacillus  coli,  204. 

pestis,  discoverj%  411. 

Bacot,  a.  W.,  375,  376,  391,  393, 
395,  409,  412,  444,  445,  446. 

Bacteria,  distinguished  from  Proto- 
zoa, 27;  relation  to  trachoma, 
194;  and  intestinal  worms,  204; 
relation  to  filarial  diseases,  305- 
306;   food  of  Aedes  calopus,  446. 

Bacterium  tularense,  transmitted  by 
fleas,  413;  by  deer  flies,  489. 

Badger,  host  of  Pulex  irritans,  414. 

Bagdad,   oriental  sore,  85,  88,  471. 

Bagshawe,  a.  G.,  503. 

Bahr,  p.  H.,  303. 

Baking  soda,  for  mites,  335,  339. 

Balanitis,  cause  of,  73a;  treatment, 
73b. 

Balantidial  dysentery,  129. 

Balantidium  coh,  discovery,  7,  37; 
115;  126-127;  description,  126; 
pathogenicity,  treatment  and 
prevention,  127. 

Balkans  relapsing  fever,  43,  46. 


INDEX 


539 


Balsam  of  Peru,  for  itch,  346. 

Baltic  countries,  Diphyllobothrium 
latus   in,   246. 

Bancroft,  Th.,  7. 

Banks,  N.,  333,  339,  523,  524. 

Barbados,  home  of  "millions,"  461. 

Barbeiro,  see  Triatoma  megista. 

Barber,  M.  A.,  206. 

Barlow,  N.,  117,  132,  281. 

Barrett,  M.  T.,  142. 

Barton,  179. 

Bartonella  bacilliformis,  168;  179- 
181;   360. 

Basal  granule,  30. 

Basile,  C,  84. 

Bass,  C.  C,  9,  149,  164. 

Bats,  Cimex  in,  372,  375;  trypano- 
some  disease  of,  carried  by  Cimex 
jyipistrelli,  378;  natural  enemies 
of  mosquitoes,  462;  natural 
enemies  of  tsetse  flies,  503. 

Baton,  H.,  378. 

Beauperthuy,  L.  D.,  322. 

Bedbugs,  and  relapsing  fever,  45,  46; 
378;  and  kala-azar,  77-78,  377; 
and  Leishmania  infantum,  83; 
and  oriental  sore,  86,  377-378; 
and  Trypanosoma  cruzi,  112, 
370,  378;  Rickettsia  in,  185; 
371-379;  general  structure, 
371;  odor,  371-372;  species, 
372-373;  habits,  373-375;  effect 
of  bites,  374;  hosts,  374-375; 
life  history,  375-376;  and  dis- 
ease, 376-379;  and  bubonic 
plague,  378-379;  remedies 
and  prevention,  383;  fumi- 
gation of,  385-386. 

Bee  eater,  natural  enemy  of  tsetse 
flies,  503. 

Beef  tapeworm,  see  Tcenia  saginata. 

Beetles,  hosts  of  Gigantorhynchus 
hirudinaceus,  284;  natural 
enemies  of  mosquitoes,  462. 

Belascaris  cati,  282. 

Belgium,  Tydeus  molestits,  341. 

Bello  Herizonte,  eradication  of 
Chagas'  disease,  114. 


Beta-naphthol,  for  Giardia  infec- 
tions, 125;  for  hookworm  in- 
fections, 264;  ointment  for  itch, 
346. 

Bete  rouge,  335,  336. 

Bi-flagellate  Protozoa,  of  intestine, 
117-118. 

BiLHARz,  Th.,  7. 

Bihary  fever,  of  horses,  168. 

Binucleata,  30, 

Bird  lice,  see  Mallophaga. 

Birds,  hosts  of  Cimex,  372;  chief 
prey  of  Culex  quinquefasdatus, 
449;  as  food  for  tsetse  flies,  494, 
495;  natural  enemies  of  tsetse 
flies,  503;  blood-sucking  mag- 
gots in  nests  of,  511. 

BiSHOPP,  F.  C,  422. 

Bismuth  salicylate,  for  Giardia  in- 
fections, 125. 

Bismuth  subnitrate,  for  amebic  dys- 
entery, 137. 

Biting  flies,  see  Fhes,  blood-sucking. 

Black  corsair,  see  Melanolestes 
pidpes. 

Black  drongo,  natural  enemy  of 
tsetse  flies,  503. 

Blackflies,  and  espundia,  92;  and 
Onchocerca  coBCutiens,  311;  mouth- 
parts,  327,  478;  478-484;  de- 
scription, 478-479;  life  history, 
479-481;  annoyance,  481-483; 
and  disease,  483;  control,  483- 
484. 

Blackheads,  relation  of  Demodex  to, 
347. 

Blacklock,  B.,  494,  496. 

Black  sickness,  see  Kala-azar. 

Black  vomit,  in  yellow  fever,  71. 

Blackwater  fever,  161-162. 

Bladderworms,  types  of,  236;    dam- 
age done  by,  236-237. 
beef  bladderworms,  see  Cysticercus 

hovis. 
pork  bladderworms,  see  Cysticer" 
cus  cellulosce. 

Blanfordia,  host  of  Schistosoma  jon 
ponicum,  219, 


540 


INDEX 


Blepharoplast,  29;  see  also  Para- 
basal body. 

Blood,  immunity  reactions,  20-22; 
relation  to  anaphylaxis,   23-24. 

Blood  corpuscles,  white,  see  Leuco- 
cytes. 

Blood  flukes,  discovery,  7,  8;  213- 
220;  relation  of  sexes,  213; 
possibility  of  introduction  into 
United  States,  219-220.  See 
also  Schistosoma. 

Bloodsuckers,  see  Leeches. 

Blowflies,  maggots  parasitic  on  birds, 
511. 

Bodo,  115;  117-118. 

Bolivia,  oriental  sore,  87. 

Bombay,  relapsing  fever,  43. 

Bont  tick,  see  Amblyomma  hebrceum. 

Borax,  and  calcium  borate  for  treat- 
ing manure,  508. 

Botflies,  mouth  parts,  464;  in  human 
skin,  513-516;  and  intestinal 
myiasis,  524. 

BozzoLo,  C,  8. 

Braun,  M.,  36. 

Brazil,  yaws,  63;  kala-azar,  77; 
espundia,  90,  488;  trypanoso- 
miasis, 94,  108-114;  bug-proof 
houses,  114;  Trichomonas 
pathogenic,  121;  Enteromonas 
hominis,  122;  hookworm  dis- 
ease, 255;  (Esophagostomum 
stephanostomum  thomasi,  283; 
Filaria  magalhaesi,  308;  Tria- 
toma,  380-381;  Anopheles  cruzi, 
habits,  442;  Dermatohia  and 
mosquitoes,  452,  453. 

Breakbone  fever,  see  Dengue. 

Breinl,  a.,  73d. 

British  Columbia,  tick  paralysis, 
358-359;  Dermacentor  venustus, 
363. 

British  Guiana,  Sparganum  mansoni, 
252;  hookworm  disease,  262; 
filarial  infections,  308. 

British  Isles,  see  Great  Britain. 

British  Plague  Commission,  411,  412. 

British  Royal  Commission  on  Vene- 


real Diseases,  report,  50,  58, 
59-60. 

British  Trench  Fever  Commission, 
187,  397,  399. 

Bronchitis,  caused  by  spirochsetes, 
71. 

Bruce,  D.,  7,  98,  108,  397. 

Brumpt,  E.,  83. 

Buba  braziliensis,  89. 

Bubalis  caffer,  host  of  Glossina 
morsitans,  500. 

Bubonic  plague,  see  Plague. 

Buenaventura,   yellow  fever  in,   70. 

Buffalo,  host  of  Glossina  morsitans. 

Buffalo  gnats,  see  Blackflies. 

Bugs,  see  Hemiptera. 

Bulgaria,  typhus  in,  398. 

Bullinus  contortus  and  B.  dyhowskiiy 
intermediate  hosts  of  Schisto- 
soma in  Egypt,  215,  216,  217. 

Bursa,  of  hookworms,  256. 

Butter,  on  clothing  to  prevent  lousi- 
ness, 402. 

Byam,  Maj.  W.,  397. 

Bythinia  striatula,  var  japonica,  inter- 
mediate host  of  Clonorchis,  226. 

Cachexia,  malarial,  161,  162;  treat- 
ment, 164. 

Cairo,  prevention  of  Schistosoma  in- 
fections, 216b. 

Calabar  sweUings,  309. 

Calandruccio,  S.,  284. 

Calcium  borate,  and  borax  for  treat- 
ing manure,  508. 

California,  hookworm  in  mines,  262; 
hookworm  introduced  by  Hin- 
dus, 268;  Dermacentor  occiden- 
talis,  358,  363;  Ornithodorus 
coriaceus,  364-365;  plague  in 
ground  squirrels,  411;  Pulex 
irrilans,  415;  Ceratophijllus  acu- 
tus,  418. 

Calkins,  G.  N.,  33. 

Calliphora  vomitoria,   cause   of  my- 
iasis, 521. 
erythrocephala,    cause   of   myiasis, 
521. 


INDEX 


541 


Calomel,  for  Giardia  infections,  125. 

Camel,  and  oriental  sore,  86;  host  of 
Trichostrongylus  instabilis,  282; 
host  of  Ornithodorus  savignyi, 
361;  eldebab,  487. 

Camphor,  for  red-bug  rash,  336; 
repellent  for  mosquitoes,  455. 

Canada,  blackflies,  479,  481,  482. 

Capitulum,  of  ticks,  354. 

Carapatos,  see  Ornithodorus  moubata 
and  0.  turicata. 

Carbolic  acid,  for  head  lice,  401;  to 
remove  Dermatobia  from  skin, 
515. 

Carbon  bisulphide,  fumigation,  386; 
for  fumigation  of  body  lice,  401, 
402. 

Carpenter,  G.  D.  H.,  494. 

Carriers,  definition,  19,  21;  in  ame- 
bic dysentery,  136. 

Carrion,  D.,  178. 

Carrion's  fever,  see  Oroya  fever. 

Carroll,  J.,  70,  443. 

Castellani,  a.,  121,  307,  340. 

Castor  oil,  for  Giardia  infections, 
125;  in  treatment  of  hookworm 
infections,  264. 

Cats,  and  infantile  kala-azar,  82; 
and  Giardia,  125;  hosts  of 
Ojdsthorchis,  225;  Dipylidium 
caninum,  245;  fewer  parasites 
than  dogs,  266;  trichina,  288; 
^^oUsdres  cati,  343;  and^edbugs, 
375;  "-fleas,  416-417;  "^chidno- 
phaga  gallinacea,  420;  destruc- 
tion of  fleas  on,  422-423. 

Cattle,  hosts  of  spotted  fever  tick, 
189;  Paramphistomum  cervi, 
229;  Tcenia  saginata,  240;  hy- 
datids, 248,  250;  hosts  of  Der- 
macentor  venustus,  363;  hosts  of 
stable-flies,  505;  Dermatobia  in, 
513;  warble-flies,  515-516. 

Central  America,  relapsing  fever,  46; 
checking  of  yellow  fever  epi- 
demic, 72;  mal-de-boca,  73a; 
trypanosomes  in  Triatoma,  108, 
112,  380-381;  use  of  shoes,  265; 


work  of  Hookworm  Commis- 
sion, 268;  bete  rouge,  335; 
Ornithodorus,  361;  Triatoma, 
379,  380,  381;  other  Reduviidae, 
382;  chiggers,  418,  419;  Ana- 
pheles  eiseni,  habits,  441;  yel- 
low fever  mosquitoes  breeding 
in  holy-water  fonts,  445;  Der- 
matobia carriers,  452,  453. 

Centrosome,  in  Protozoa,  see  Basal 
granule. 

Ceratophyllus,  cysticercoids  in,  243; 
and  plague,  412. 
acutus,  and  plague,  413,  418. 
fasdatus,  life  history,  409;   haoits, 

etc.,  417-418 
gallinoe,  417. 
silantiev/i,  and  plague,  413. 

Ceratopogon,  475,  477. 

Ceratopogoninae,  474,  475,  476. 

Cercaria,  211. 

Cercomonas,  115,  117-118. 

Cerebrospinal  fluid,  spirochaetes  in, 
49,  57;  trypanosomes  in,  104; 
trichina  in,  290. 

Cerebrospinal  meningitis,  animal  ex- 
perimentation with,  10. 

Cerodon  rupestris,  host  of  Triatoma 
chagasi,  381. 

Cestoda,  198;    see  also  Tapeworms. 

Ceylon,  Necator  ameficanus,  255; 
beta-naphthol  used  for  hook- 
worm infections,  264;  land- 
leeches,   319;    copra  itch,   340. 

Chaetopoda,  199. 

Chagas,  C,  8,  94,  110,  111,  112. 

Chagas'  disease,  108-114;  course  of, 
113-114;  treatment  and  pre- 
vention, 114. 

Chancre,  54. 

Chandler,  A.  C,  212,  245,  285,  461. 

Chaparro  amargosa,  for  intestinal 
amebae,  138. 

Chatton,  E.,  140. 

Cheesefly,  see  Piophila  casei. 

Cheese-skipper,    see    Piophila   casei. 

Chelicerae,  of  Acarina,  331;  of  ticks, 
354. 


542 


INDEX 


Chenopodium,  oil  of,  for  amebic  dys- 
entery, 138-139;  for  intestinal 
flukes,  230;  for  tapeworms, 
237;  for  hookworms,  263-264; 
specific  action,  270;  for  Ascaris, 
270,  276;  for  whipworms,  277; 
for  pinworms,  279. 

Chicken  mite,  341. 

Chickens,  and  bedbugs,  375;  and 
Triatoma,  379;  Ceratophyllus 
galliruB,  417;  Echidnophaga 
gallinacea,  420. 

Chigger,  see  Dermatophilus  pene- 
trans and  Harvest  mites. 

Chigoe,  see  Dermatophilus  penetrans. 

Chilomastix,  117. 
mesnili,  122-123. 

China,  relapsing  fever,  43;  syphilis, 
50;  kala-azar,  77;  Emhado- 
monas  sinensis,  118;  Tri- 
chomonas pathogenic,  121; 
Schistosoma  japonicum,  215; 
Schistosoma  mansoni,  218; 
lung  flukes,  220;  human  hver 
flukes,  224;  Yokagawa  yoka- 
gawa,  228;  Fasciolopsis  huski, 
229;  use  of  shoes,  265;  rat  fleas, 
417;  malaria-carrying  Ano- 
pheles, 441;  transmission  of 
anthrax  by  tabanids,  488. 

Chinese  fluke,  see  Clonorchis  sin- 
ensis. 

Chironomidse,  and  uta,  86,  477; 
.  473-477;  description,  473-475; 
habits,  475;  life  history,  475- 
476;  annoyance,  476;  as  dis- 
ease carriers,  476-477;  control, 
477. 

Chlamydophrys     stercorea,     132-133. 

Chlamydozoa,  170,  191-195. 

Chloroform,  for  hookworm  infec- 
tions, 264;  as  an  anthelmintic, 
270-272;  in  milk  for  myiasis  of 
nose,  ear,  etc.,  523. 

Chlorosis,  255. 

Chceromyia,  512-513. 

Christiansen,  E.,  124. 

Christopherson,  J.  B.,  216a. 


Chromidia,  28. 
Chrysomyia  bezziana,  521. 

macellaria,  see  Cochliomyia. 
Chrysopsj  and  Loa  lea,  309-310,  486, 
487,  489;  trap  for,  490. 
dimidiata,  489. 
discalis,  489. 
silacea,  489. 
Chyluria,  filarial,  305. 
Ciha,  30. 
Ciliata,  cilia  in,  30;   35;   36;   human 

parasites,  126. 
Cimex,  371,  372;   see  also  Bedbugs. 
houeti,  373. 

hemipterus,  and  kala-azar,  77-78, 

377;     characteristics,    372-373. 

ledularius,     characteristics,     372- 

373;  hosts,  374-375. 
pipistrelli,  378. 
rotundatus,  see  C.  hemipterus. 
Cimicidse,  characteristics,  371. 
Cinchona,  see  Quinine. 
Cinchonization,  see  Quininization. 
Cirri,  30. 

Cirrus  pouch,  232. 
Citellus  heecheyi,  and  plague,  413. 
Citronella,  oil  of,  repellent  for  mos- 
quitoes, 455. 
Civet  cats,  hosts  of  Ancylostoma  cey- 

lanicum,  255. 
Civil  War,  fly  maggots  in,  521. 
Clarke,  F.  C,  414. 
Clonorchis  endemicus,  =  sinensis,  225. 
sinensis,  discovery,  7;    211,  224- 
225;   life  history,  226. 
Cnidosporidia,  36. 
Cocaine,  for  leeches,  318. 
Coccidians,   168;    170-173;    life  his- 
tory, 170-172;  in  man,  172-173. 
Coccidium  seeberi,  174. 
Coccoid  bodies  in  spirochsetes,  39. 
Cochliomyia  macellaria,  in  espundia 
sores,  90;    egg-laying,  464,  519; 
619-521;    description,  519;    ef- 
fects, 520-521;    treatment,  523. 
Cockle  bur,  mites  on,  341. 
Cockroach,  and  Davainea  madagas- 
cariensis,     244;      and     Monili- 


INDEX 


543 


formis  moniliformis,  284. 
Ccsnurus,  235. 

Cold     storage,    effect     on    bladder 
worms,   238;    on  trichina,  295; 
on  Clonorchis  larvae,  227. 
Colemanite,  and  borax  for  treating 

manure,  508. 
Colombia,  relapsing  fever,  46;  spiro- 
chsetal  bronchitis,   73b;    Balan- 
tidium   infections,    127;     yellow 
fever,    70;     hookworm    disease, 
254. 
Columbacz  fly,  482. 
Combs,  on  fleas,  404,  408. 
Compulsory  notification,  of  venereal 

disease,  60. 
Cone-nose,  see  Triatoma. 
Congo,  rubber  industry  and  sleeping 
sickness,  107;  Porocephalus,  351. 
Congo   floor   maggot,    see   Auchero- 

myia  luteola. 
Contractile  vacuole,  31. 
Copepods,  intermediate  hosts  of  Di- 

phyllobothrium,  246-247. 
Copper  sulphate,  for  destruction  of 

snails,  212. 
Copra  itch,  340. 

Cordylobia   anthropophaga,    616-518; 
deposition  of  eggs,  517;    devel- 
opment   of     maggot    and    life 
history,  518;   prevention,  518. 
rodhaini,  518-519. 
Corethra,  425. 
Corethrinse,  437. 
Cornwall,  J.  W.,  377,  378. 
Corrosive    sublimate,    see    Mercuric 

chloride. 
Corsica,  phlebotomus  flies,  468. 
Councilmxinia,  129. 

lafleun,  129,  131,132,  140,  141. 
Coyote,  host  of  Opisthorchis  pseudo- 

felineus,  225. 
Crabs,    relation    to    lung   flukes,    8, 

222-223. 
Cragg,  F.  W.,  374,  416. 
Craig,  C.  F.,  132,  143,  145,  301,  448. 
Craigia,  hominis,  132. 
migrans,  132. 


Craneflies,  allied  to  mosquitoes,  425. 

Crawley,  H.,  176. 

Crayfish,  possible  host  of  lung  flukes, 

223. 
Creolin,  for  removal  of  ticks,  367; 
for  fumigation,  386;    to  destroy 
fleas,  422-423. 
Cresol,   for  killing  Schistosoma  cer- 
cariae  in  water,  217;    for  body 
lice,  402;    for  chiggers,  420;    to 
destroy  mosquito  larvse,  459. 
Cresyl,    for    fumigation,    386;     for 
fumigation  of  mosquitoes,  456. 
Crithidia,  75;   stage  of  trypanosome, 

95-96. 
Crocodiles,    fed   on   by   tsetse   flies, 

494,  499. 
Cruickshank,  J.  A.,  306. 
Crustacea,  first  intermediate  host  of 
Diphyllobothrium      latus,      246; 
324;     see   also   Crabs,    Shrimp, 
Cyclops. 
Ctenidia,  404,  408. 
Ctenocephalus    canis,    and    infantile 
kala-azar,    83,    413;     hfe   cycle, 
410;    and  Dipylidium  caninum, 
414;  habits,  etc.,  416-417. 
felis,  life  cycle,  409;    habits,  etc., 
416-417. 
Cidex,  intermediate  host  of  Filaria 
bancrofti,  301;  and  bird  malaria, 
438. 
fatigans,    see    C.  quinquefa^ciatiis. 
pipiens,   resemblance  of  C.  quin- 

quefasciatus  to,  448. 
quinquefasdatus,  and  dengue,  183, 
448;    and  Filaria  bancrofti,  301; 
description,  etc.,  448-449. 
terrOans,  434. 
Culicidae,  characteristics,  425. 
Cuhcinae,  437. 
Cuhcini,  437. 

Culicoides,  habits  of  larvae,  475;   an- 
noyance, 476. 
Cultivation,  of  animal  parasites,  9. 
Cyclasterion  scarlatinoe,  191. 
Cyclops,    and    guinea- worm,    inter- 
mediate   host    of    Diphylloboth- 


544 


INDEX 


Hum,  246-247;  312,  313-314. 
Cyclorrhapha,  465,  466. 
Cyprinodontidse,  natural  enemies  of 

mosquitoes,  460. 
Cysticercoid,  nature  of,  235. 
Cysticercus,  nature  of,  235. 

bovis,   thermal   death   point,   237- 

238;   effect  of  cold  storage,  238; 

description,  240. 
ceUulosce,     thermal     death     point, 

237-238;  effect  of  cold  storage, 

238;     description,    241;     hosts, 

241-242;   in  man,  251. 
Cytopyge,  31. 
Cytoryctes    variolce,     170;     see    also 

guarneiri  bodies. 
Cytostome,  31. 

Dahomey,  absence  of  sleeping  sick- 
ness in,  501. 
Da  Matta,  a.,  92. 
Darling,  S.,  129,  175. 
Darwin,  Chas.,  4,  381. 
Dasypus  novemcinctus,  host  of  Try- 
panosoma cruzi,  112. 
Datura   stramonium,   for   fumigation 

of  mosquitoes,  4^6. 
Davainea  madagascariensis,  244. 

formosana,  244. 
Deer,  host  of  Pulex  irritans,  414. 
Deerfly,  see  Chrysops. 
DeKruif,  p.  H.,  23-25. 
Demarquay,  J.  N.,  7. 
Demodecidae,  333,  346. 
Demodex  folliculorum,  346-348;    life 
history,  347;    and  leprosy,    347. 
Dengue,  relation  of  mosquitoes  to,  8, 
183,  448-449;  parasites  of,  182- 
183;    182-184;    prevention,  184. 
De  Raadt,  O.  L.  E.,  399,  417. 
Derwucentor,     366;      Rickettsia     in, 
185,  186. 
andersoni,  see  D.  venustus. 
ocddentalis,    effects   of   bite,   358- 
359,   366;    possible   transmitter 
of  spotted  fever,  363,  366-367. 
variabilis,  367. 
venustus,  transmission  of  spotted 


fever,  188-189;    and  tick  paral- 
ysis, 358;    description,  361-363. 

Dermacentroxeny^  rickettsi,  188,  191. 

Dermanyssus  gallince,  341. 

Dermatobia  hominis,  and  mosquitoes, 
451-453,  514;  transmitting 
mosquitoes,  453;  513-515; 
description,  513-514;  manner 
of  reaching  host,  514;  effects, 
514-515. 

Dermatophilus  penetrans,  418-420. 

Deschiens,  R.,  125. 

De  Silva,  p.,  83. 

Desvoidea  obturbans,  and  dengue,  183, 
448. 

Diaptomu^,  intermediate  host  of  Di- 
,  phyllobothrium,  246-247. 

Dibothriocephalidse,  larvae  of,  235; 
characteristics,  239;  important 
species  of,  245-247;  Sparganum 
larva  of,  251. 

Dibothriocephalus,  see  Diphyllo- 
bothrium. 

Dicrurus  ater,  natural  enemy  of 
tsetse  flies,  503. 

Diemyctylus  torosus,  natural  enemy 
of  mosquitoes,  461. 

Dientamwba,  132. 
fragilis,  132,  142. 

Diodophijme  renale,  200. 

Diphyllobothrium  latus,  246-247. 
cordatus,  247. 

Diplocercomonas,  122. 

Diplogonoporus  grandis,  247. 

Diplozoa,  26. 

Diptera,  326;  characteristics,  330; 
425;  used  by  Dermatobia,  452, 
514;  463-464;  importance, 
463;  general  structure,  463- 
464;  life  histories,  464-466; 
classification,  466;  parasites  on 
tsetse  fly  pupae,  503;  and  my- 
iasis, 509. 

Dipylidium  caninum,  245;  and  fleas, 
414,  415,  417. 

Dirt-eating,  in  hookworm  disease,  262. 

Diseases,  conquest  of,  2;  ignorance 
of,    4;     causation   by   germ,   6; 


INDEX 


545 


transmission  by  arthropods,  7-8, 
322-323. 

Disinfection,  of  mosquito  bites,  307; 
of  tick  bites,  367;  to  eradicate 
lousiness,  402-403. 

Dim,  425. 

Dixon,  S.  G.,  462. 

DoANE,  R.  W.,  414. 

DoBELL,  C,  130,  131,  132,  133,  134, 
140,  142,  146a,  172. 

DoERR,  R.,  470. 

Dog  flea,  see  Ctenocephalus  canis. 

Dogs,  and  infantile  kala-azar,  82,  83; 
and  oriental  sore,  86;  Trypano- 
soma gambiense  in,  108;  host  of 
Trypanosoma  cruzi,  112;  sus- 
ceptible to  lung  fluke  infections, 
220;  host  of  Clonorchis  sinensis, 
224;  host  of  Opisthorchis,  225; 
Dipylidium  caninum,  245;  host 
of  Diphyllobothrium  cordatus, 
247;  Echinococcus  granulosus , 
248,  250-251;  hosts  oCHncylo- 
stoma  ceylanicum,  255;  more 
parasites  than  cats,  266;  tri- 
china, 288;  ^emodex,  347; 
^^iAnguatula  rhiriaria,  349-350; 
Dermacentor  variabilis,  367;  and 
bedbugs,  375;  inabihty  of  hu- 
man lice  to  draw  blood  from, 
393;  host  oi^Pulex  irritans,  414; 
fleas,  416-417;  Echidnophaga 
^allinucea,  420;  destruction 
of  fleas  on,  422;  ^^ermatobia  in, 
513;  ^ordylobia  anthropo- 
phaga  in,  518. 

Dog  ticks,  see  Dermacentor  variabilis 
and  Ixodes  ricinus. 

Dongola,  blackflies  in,  482. 

Donovan,  C,  7,  74,  377. 

Dracunculus  medinensis,  311-314; 
distribution,  311;  life  history, 
312-313;  extraction  and  pre- 
vention, 314. 

Dragon-flies,  natural  enemy  of  tsetse 
flies,  503. 

DuBiNi,  A.,  7. 

Ducks,  natural  enemies  of  mosqui- 


toes, 462. 
Dumdum  fever,  see  Kala-azar. 
DuTCHER,  B.  H.,  305. 
DuTTON,  J.  E.,  7,  8,  359. 
Dwarf   tapeworm,   see   Hymenolepis 

nana. 
Dyar,  I.,  429,  437,  444,  447,  458. 
Dysentery,   types  of,    135;    role  of 

amebae,  135-136. 
Dysentery    ameba,    see    Endamceba 

histolytica. 
Dysodius  lunatus,  382-383. 

Ear  tick,  see  Otiobius  megnini. 

East  Coast  fever,  of  cattle,  168. 

East  Indies,  gangosa,  64;  black- 
water  fever,  161;  land-leeches, 
319;  Porocephalus  monili- 
formis, 351;  transmission  of 
malaria,  441;  Anopheles  in 
coral   reef   pools,    442. 

Echidnophaga  gallinacea,  420. 

Echinorhynchus  hominis,  284;  see 
also  Monilifortnis. 

Echinococcus  granulosus,  236;  240- 
251;  distribution,  248;  adult 
and  hfe  history,  248;  develop- 
ment of  hydatids,  248-249; 
other  species  of  Echinococcus, 
250;  prevention,  250-251. 

Echinostomum  ilocanum,  228-229. 
malayanum,  229. 

Ectoplasm,  29. 

Ecuador,  hookworm  disease,  262. 

Education,  present  need,  3-4;  con- 
cerning sex  hj^giene,  62;  con- 
erning  sanitation,  268-269. 

Eelworms,  see  Ascaris. 

Egypt,  Embadomonas  intestinalis, 
118;  amebae  in  sand,  128; 
Schistosoma  hcematobium,  213- 
214,  215,  216b;  Heterophyes 
heterophyes,  228;  Paramphist- 
omum  cervi,  229;  Sparganum 
mansoni,  252;  hookworm  dis- 
ease, 255;  work  of  Hookworm 
Commission,  268;  Trichostron- 
gylus    instabilis,    282;     Xenop- 


546 


INDEX 


sylla     cheopis,     417;      breeding 
places  of  Phlebotomus,  468,  473. 

Ehrlich,  p.,  8,  47,  49,  56. 

Eimeria,  in  man,  172-173. 
oxyspora,  172. 
snijderi,  172. 
stiedoe,  in  man,  172. 
wenyoni,  172. 

El  debab,  487. 

Elephantiasis,  304-305;  relation  of 
bacteria  to,  305-306;  treatment, 
306;  and  Onchocerca  volvulus  in 
Congo,  311. 

Elephantoid  fever,  305. 

Elk,  host  of  Dermacentor  venustus, 
363. 

Ellis,  A.  W.  M.,  57. 

El  Marg,  Schistosoma  hoematohium, 
214,  215. 

Emhadomonas,  115,  117. 
intestinalis,  118. 
sinensis,  118. 

Emetin,  discovery,  8;  not  effective 
for  Giardia,  125;  for  Balanti- 
dium  infections,  127;  nature  of, 
137;  in  amebic  dysentery,  137- 
138;  effects  on  other  amebae, 
141;  in  pyorrhea,  145,  146a. 

Emrich,  W.,  138,  139. 

Encapsulation,  20-21;  of  trichina, 
291. 

Encystment,  34. 

Endamceba,  in  jaw  lesion,   121;    de- 
cription  of  genus,  129. 
buccalis,  see  E.  gingivalis. 
colly  132;    compared  with  E.  histo- 
lytica,   133;     135;     description, 
140-141. 
gingivalis,    142-146b;     relation   to 
pyorrhea,    142,    144-146a;     de- 
scription, 143;    relation  to  ton- 
sihtis  and  goitre,  146;   effect  of 
emetin  on,  146a. 
histolytica,   115,    129;     description 
and  life  history,  133-134;   com- 
pared  with   E.    coli,    133;    and 
disease,  135-136;   effect  of  eme- 
tin on,  137-138. 


muris,  140. 

nana,  see  Endolimax  nana. 

Endolimax,     description     of     genus, 
129. 
nana,  130,  132,  135, 141. 

Endomixis,  33-34. 

Endoplasm,  29. 

Endotoxins,  24. 

Entamoeba,  see  Endamceba. 

Enteromonas,  117. 
hominis,  122. 

Eosinophiles,  increase  with  worm  in- 
fections, 203. 

Epimys    norvegicus,   and    plague    in 
Europe,  411. 
rattus,    and    plague    in    Europe, 
411. 

Epipharynx,  326. 

Epsom  salts,  see  Magnesium  sul- 
phate. 

Erdmann,  R.,  175. 

Eriocheir  japonicus,  intermediate 
host  of  lung  fluke,  222. 

EscoMEL,  P.,  117,  121,  125. 

Espundia,  89-92;  distribution,  89; 
parasites,  89;  skin  sores,  89; 
mucous  membrane  ulcerations, 
90;  treatment,  91-92;  preven- 
tion, 92. 

Ether,  for  body  hce,  401. 

Eucalyptus,  oil  of,  for  hookworm  in- 
fections, 264;  for  body  lice,  401; 
for  fleas,  422;  for  phlebotomus 
flies,  473. 

Eupodidse,  333,  341. 

Europe,  plague  in,  2,  411;  relapsing 
fever,  42,  44',  378;  introduction 
of  syphilis,  48;  infectious  jaun- 
dice, 65;  amebic  dysentery, 
134;  blackwater  fever,  161; 
dengue,  182;  trench  fever,  187, 
399;  Opisthorchis  felineus,  225; 
Hymenolepis  nana,  242;  hook- 
worm disease,  255;  Ancylos- 
toma  duodenale,  *255;  hookworm 
in  miners,  265;  trichina,  287, 
288;  Filaria  bancrofti,  299; 
Hcemopis,   317;    red-bugs,    336; 


INDEX 


547 


Norwegian  itch  343;  Demodex 
folliculorum,  347;  Linguatula 
rhinarixi,  350;  Argas  reflexus, 
364;  Ixodes  ridnus,  367;  ty- 
phus, 186,  398;  origin  of  Pidex 
irritans,  414;  Ceratophyllus  sp., 
417,  malaria-carrying  Ano- 
pheles, 441;  Phlebotomus  papa- 
tdsii,  470;  control  of  Phleboto- 
mus, 473;  Columbacz  fly,  482; 
Wohlfartia  magnifica,  521- 
522;  Fannia,  524,  See  also  ge- 
ographic subdivisions. 

European  War,  typhus  in,  2,  398; 
infectious  jaundice,  68;  amebic 
dysentery,  131. 

Eustrongylus  gigas,  see  Dioctophyme 
renale. 

Evans,  J.  S.,  144. 

EwiNG,  H.  E.,  332. 

Faeces,  search  for  parasite  eggs  in, 

206,  272. 
Fannia,  characteristics  of  larvae,  509; 

and  intestinal  myiasis,  524-526; 

effects    of    myiasis    caused    by, 

527. 
canicularis,  and  intestinal  myiasis, 

524-526;       and      myiasis      of 

urinary  passages,  528. 
scalaris,    and    intestinal    myiasis, 

524-526;    and    myiasis   of    uri- 
nary passages,  528. 
Fantham,  H.  B.,  39,  102,  174. 
Farmers   responsibility  for  trichini- 

asis,  296. 
Fasdola  hepatica,   discovery   of  life 

cycle,  7;    life  history,  209-211; 

in  man,  224. 
Fasdolopsis  buski,  229-230. 
Faust,  E.  C,  118,  119. 
Fibrolysin,  in  elephantiasis,  307. 
Fiji   Islands,   yaws   in,   63;     Filaria 

bancrofti,  301. 
Filaria,  discovery,  7,  298;    relation 

of    mosquitoes    to,    7,   301-303, 

449-451;   298-314;     prevalence, 

298-299. 


bancrofti,    299-307;     distribution, 
299;  life  history,  299-303;  peri- 
odicity, 300-301;    cycle  in\nos- 
quitoes,    301-303,    450;     trans- 
mission, 303;  pathogenic  effects, 
303-306;     treatment   for,    306- 
307;  prevention,  307. 
demarquaii,  see  F.  juncea. 
juncea,  308,  450. 
loa,  see  Loa  loa. 
magalhaesi,  308. 
Persians,  301,  450. 
philippinensis,  307-^308,  450. 

Filarial  diseases,  303-306;  elephanti- 
asis, 304-305;  chyluria,  305; 
relation  of  bacteria  to,  305- 
306;  treatment,  306-307;  pre- 
vention, 307. 

FiNOCCHIARO,  F.,  73c. 

Fish,  intermediate  hosts  of  Clonor- 
chis  sinensis,  226;  of  Opisthor- 
chis,  226-227;  of  Dibothrio- 
cephalidoe,  245;  of  Diphyllo- 
hothrium  latus,  247;  relation 
to  Sparganum  mansoni,  252; 
relation  to  Sparganum  prolif- 
erum,  253. 

Fish  oil,  repellent  for  tabanids,  489. 

Fish  tapeworm,  see  Diphyllobothrium 
latus. 

Flagellata,  flagella  in,  29,  35,  36. 

Flagellates,  chlorophyll-bearing,  27; 
of  blood-sucking  insects  in  verte- 
brates, 74,  75. 

Flagellum,  29. 

Flame  cells,  197. 

Flatworms,  196-198. 

Fleas,  and  infantile  kala-azar,  83, 
413;  Rickettsia  in,  185;  inter- 
mediate hosts  of  Dipylidium 
caninum,  245,  414;  fumiga- 
tion, 386,  421;  general  struc- 
ture, 404-407;  classifica- 
tion, 407;  identification,  408; 
life  history,  408-410;  habits, 
410;  and  disease,  410-414;  and 
plague,  410-413;  and  typhus, 
414;   human  flea,  414-415;   dog 


548 


INDEX 


and  cat  fleas,  83,  416-417;-  rat 
and  squirrel  fleas,  417-418;  chig- 
'gers,  418-420;  sticktight  flea, 
420-421;  prevention,  421-423; 
traps,  421. 

Fleshflies,  and  Sarcosporidia,  175; 
and  myiasis  of  wounds,  521- 
522;  description,  522;  and  in- 
testinal myiasis,  526-527. 

Flexner,  S.,  10. 

Flies,  see  also  Diptera. 

blood-sucking,  mouthparts,  327, 
464;  importance,  463;  see  also 
various  groups  and  species, 
non-blood-sucking,  and  oriental 
sore,  86;  and  espundia,  92; 
role  in  transmission  of  Giardia, 
125;  and  tapeworm  eggs,  240; 
mouthparts,  327,  464. 

Flood  fever,  see  Kedani. 

Florida,  prevention  of  malaria  by 
screening,  167;  Sparganum 
proliferum,  252-253. 

Flukes,  207-230;  general  anatomy, 
207-208;  reproduction,  208; 
life  history,  208-211;  parasitic 
habitats,  212;  control,  212;  see 
also  Blood  flukes.  Lung  flukes. 
Liver  flukes.  Intestinal  flukes. 

Flury,  F.,  202,  290,  293. 

Fly-belts,  106,  492-493. 

FoNSECA,  O.  O.  R.  da. 

Foot-and-mouth  disease,  parasite  of, 
76,  169,  193. 

Forcipomyia,   and  uta,   86;    habits, 
475,  477. 
townsendi,  and  uta,  86,  477. 
utce,  and  uta,  86,  477. 

FoRDE,  R.  M.,  7. 

Formaldehyde,  for  fumigation,  386; 
to  destroy  flea  eggs,^  421;  to 
repel  phlebotomus  flies,  473. 

Formalin,  see  Formaldehyde. 

Formosa,  transmitter  of  dengue,  183, 
448;  lung  flukes,  220,  222; 
Yokagawa  yokagawa,  228;  Da- 
vainea  formosana,  244;  aquatic 
leeches,  317. 


Foster,  W.  D.,  263,  264,  270,  272, 
274,  275,  276. 

FOURNIER,  50. 

Fowl  tick,  see  Argas  persicus. 

Fracastorio,  G.,  6. 

Frambesia,  see  Yaws. 

France,  amebic  dysentery,  135; 
trench  fever  among  troops,  399; 
Wohlfartia  magnifica,  522 

Francis,  E.,  489. 

Frankel,  S.,  402. 

French  Guiana,  Onchocerca,  310. 

French  Yellow  Fever  Commission, 
444. 

Fricks,  L.  D.,  190. 

Frontal  lunule,  465. 

Fuller,  C,  516,  517. 

Fumigation,  for  ticks,  369;  hydro- 
cyanic acid,  383-386;  sulphur, 
386;  carbon  bisulphide,  386; 
cresyl,  386;  formaldehyde,  386; 
for  fleas,  421;  for  mosquitoes, 
456. 

FuTAKi,  K.,  73. 

Gadflies,  see  Tabanidse. 

Gallipoli,  Giardia,  in  soldiers  from, 
123,  125;  Coccidian  infections, 
172. 

Galyl,  substitute  for  salvarsan,  65. 

Gamasidse,  see  Parasitidse. 

Gangosa,  64. 

Gasoline,  for  bugs,  383. 

Gastrodiscoides  hominis,  229. 

Gastrophilus  equi,  524. 
hcemorrhoidalis,  516. 

Gates,  Dr.  H.,  253. 

Gecko,  Algerian,  and  oriental  sore, 
86,  471. 

Geese,  host  of  Holothyrus  coccinella, 
341. 

Geographic  distribution,  of  para- 
sites, 18-19. 

Gerlach,  a.  C,,  345. 

Germany,  multilocular  hydatids, 
250;  trichina,  286;  LinguatuLa 
rhinaria  in  man,  350;  louse  pre- 
vention," 402-403. 


INDEX 


549 


Giardia,  115,  123-125;  description, 
123;  multiplication,  123-124; 
pathogenicity  and  treatment, 
125;  role  of  flies  in  transmission, 
125. 
intestinalis,  123-125. 
muris,  124;   125. 

Gibraltar,  relapsing  fever,  47. 

Gigantorhynchus    hirudinaceus,    284. 
gigas,  284. 

Gill,  A.  A.,  162. 

Giraffe,  host  of  Tamia  saginata,  240. 

GirardiniLS    pcedloides,    natural    en- 
emy of  mosquitoes,  460-461. 

GiRAULT,  A.  A.,  376. 

Glossina,   491^92;    see  also  Tsetse 

flies. 

brevipalpus,  time  of  activity,  493, 

501;    and  human  trypanosomes, 

500. 

longipennis,  time  of  activity,  493, 

501. 
morsitans,  and  Trypanosoma  rho- 
desiense,  98,  101,  497;  distribu- 
tion, 98;  fly-belts,  106,  492-493; 
499-500;  time  of  activity,  493, 
500;  habits,  493;  food,  494, 
500;  duration  of  pupal  period, 
496;  breeding  places,  496;  and 
nagana,  497;  distribution,  499; 
description,  499;  and  Trypano- 
soma gambiense,  500;  control, 
501;  attached  by  dragon-flies, 
503. 
pallidipes,  and  Trypanosoma  gam- 
biense, 500. 
palpalis,  and  Trypanosoma  gam- 
biense, 98-101,  496-497,  501; 
fly-belts,  106,  492-493,  498; 
time  of  activity,  493;  food, 
494;  498-499;  hfe  history,  495; 
breeding  places,  496;  distribu- 
tion, 498;  description,  498; 
control,  501. 
tachinoides,  time  of  activity,  493, 
498;  and  sleeping  sickness,  500; 
habitats,  500;    control,  501. 

Glyciphagus,  340. 


buski,  340. 

Gnats,  see  Chironomidae. 

Goats,  hasts  of  Linguatida  rhinaria, 
349,  unattractive  to  tsetse  flies, 
499. 

GoDDARD,  F.  W.,  229,  230. 

Goitre,  caused  by  Trypanosoma 
cruzi,  114;  caused  by  End- 
amoeba  gingivalis,  144-145;  trans- 
mitted by  Acanthaspis  svl- 
cipes,  382. 

GOLDBERGER,  J.,  8,  339,  397. 

Gomes,  J.  F.,  514. 

GONDER,  R.,  34. 

Gonzales,  E.,  217. 

GOODEY,  T.,  119. 

GoRGAs,  W.  C.,  166. 

Gorilla,  host  of  Necator  americanus, 
255;  host  of  (Esophagostomum 
stephanostomum,  283. 

Graham,  H.,  8,  448. 

Grain  mites,  see  Tyroglyphidce. 

Grassi,  B.,  284. 

Grayback,    see   Pediculus   humanus. 

Great  Britain,  syphilis  in,  50;  ame- 
bic dysenter}^,  134. 

Greece,  downfall  due  to  malaria, 
147. 

Greenland,  Diphyllobothrium  corda- 
tus,  247. 

Grocers'  itch,  340. 

Groll,  293. 

Ground  itch,  259,  260. 

Guam,  gangosa,  64. 

Guarnieri  bodies,  in  smallpox,   191. 

Guatemala,  Onchocerca  ccecutiens  in, 
311. 

Guiana,  Cimex  boueti,  373. 

Guinea-pigs,  for  experimentation, 
10;  immunization  against  in- 
fectious jaundice,  68;  host  of 
Trypanosoma  cruzi,  112,  378, 
381;  susceptible  to  trichina, 
288;  and  plague,  413. 

Guinea-worm,  see  Dracunculus  m^dv- 
nensis. 

Gumma,  54. 

Gyrinidae,  and  mosquitoes,  462. 


550 


INDEX 


Haeckel,  E.,  27. 

Hcemadipsa  ceylonica,  319. 
japonica,  320. 

HoBmaphjjsalis,  366. 

Hcematobia  serrata,  506. 

Hcematopinus  ventricosus,  inability 
to  draw  human  blood,  393. 

Hcematopota,  486. 

Hsemoflagellata,  75. 

Hcemopis,  316,  317. 

Hagler,  378. 

Hall,  M.  C,  263,  264,  270-272,  276. 

Hall,  H.  C,  393,  394. 

Haltere,  464. 

Haplosporidia,  Rhinosporidium  mem- 
ber of,  173. 

Harvard  School  of  Tropical  Medi- 
cine, South  American  expedi- 
tion, on  uta,  86;  on  Oroya 
fever,  178,  179,  180,  181. 

Harvest  mites,  333-337;  life  history, 
334;  annoyance,  335;  species, 
336;    and  kedani,  191,  336-337. 

Haughwout,  F.  G.,  121. 

Havana,  reduction  of  malaria,  166; 
reduction  of  yellow  fever,  70, 
72. 

Hawaii,  introduction  of  mosquitoes, 
435. 

Hayashi,  N.,  190. 

Head-maggot,  of  sheep,  see  (Estrus 
ovis. 

Hellebore,  for  treating  manure,  508. 

Hemiptera,  mouthparts,  326;  di- 
gestive tract,  327-328;  char- 
acteristics, 330,  370. 

Herms,  W.  B.,  364,  365,  489,  505, 
506. 

Herrick,  W.  W.,  293. 

Herrick,  G.  W.,  335,  384,  385,  387. 

Herpetomonas,  stage  of  Leishmania, 
74;  species,  75;  relationships, 
75;  in  blood  in  leishmaniasis, 
75;  developed  from  Leishmania 
donovani  in  bedbugs,  78;  in 
Anopheles  punctipennis,  78; 
stage  of  trypanosomes,  95-96; 
in  tabanids,  488. 


denocephali,    and    infantile    kala- 
azar,  83. 

Heterophyes  heterophyes,  228. 

Heteroptera,  370. 

Hindle,  E.,  187,  188. 

HiNE,  J.  S.,  490. 

Hippobosca  canina,  and  leishmani- 
asis of  dogs,  86. 

Hirudinea,  199-200;  see  ako 
Leeches. 

Hirudo,  316. 

History  of  parasitology,  6-13. 

Hogs,  Trypanosoma  gambiense  in, 
108;  and  human  intestinal  Pro- 
tozoa, 116;  and  Balantidium 
coll,  127;  Paragonimus  kellicotti, 
220;  Gastrodiscoides  hominis, 
229;  Fasciolopsis  buski,  229; 
ToBuia  solium,  240-241;  Ascaris, 
274,  275;  trichina,  286,  287,  288, 
292,  296;  Ornithodorus  turicata, 
361;  Dermatophilus  penetrans, 
418;   Dermatobia  in,  513. 

HoGUE,  M.  J.,  118. 

Holothyrus  coccinella,  341. 

Honduras,  craigiasis,  137;  Strongy- 
loides,  281. 

HooKE,  387. 

Hookworms,  economic  importance 
of,  3,  254,  262-263;  in  immi- 
grants, 5;  discovery,  7;  detec- 
tion of  ova  by  various  methods, 
206;  toxins,  203,  261;  254-269; 
history,  254-255;  local  names, 
254-255;  distribution,  255; 
description  of  species,  255-257; 
life  history,  257-260;  eggs,  258; 
mode  of  infection,  259-260; 
disease,  260-263;  dirt-eating, 
262; '  treatment,  263-264;  pre- 
vention, 264-265;  sanitation, 
265-269. 
American,  see  Necator  americanus. 
Old  World,  see  Ancylostoma  duo- 
denale. 

Hoplopsyllus  anomalus,  and  plague, 
413. 

Horseflies,  see  TabanidaB. 


INDEX 


551 


Horsehair  snakes,  popular  supersti- 
tion, 4;  see  Nematomorpha. 

Horse  leech,  316. 

Horses,  and  oriental  sore,  86; 
spotted  fever  tick,  189,  363; 
Gastrodiscoides,  229;  leeches, 
317,  319;  Ornithodorus  savignyi, 
361;  Otiobius  megnini,  365; 
surra,  487;  hosts  of  stable-flies, 
505;  hosts  of  Gastrophilus  hoem- 
orrhoidalis,  516. 

Housefly,  see  Musca  domestica. 

House  mosquito,  of  tropics,  see 
Culex  quinquefasdatus;  of 
temperate  zones,  see  Culex  pip- 
tens. 

Howard,  L.  O.,  148,  429,  437,  442, 
444,  447,  455,  458. 

HowLETT,  F.  M.,  469,  470. 

Hume,  81. 

Hyalomma,  366. 

Hydatids,  nature  of,  235,  248-261; 
distribution,  248;  life  history, 
of  Echinococcus,  248;  develop- 
ment, 248-249;  multilocular, 
250;  effects  on  host,  250;  pre- 
vention, 250-251. 

Hydrocyanic  acid,  for  fumigation, 
of  bedbugs,  383,  385;  method, 
383-385;  effectiveness,  385- 
386;  for  fleas,  421. 

Hydrogen  peroxide,  for  balanitis, 
73b. 

Hydrophobia,  see  Rabies. 

Hijmenolepis,  prevention,  238;    cys- 
ticercoids  in  fleas,  414. 
diminuta,  244. 
murina,  242, 

nana,  discovery,  7;    oil  of  cheno- 
podium    for,    237;     prevention, 
238;  242-244. 
nana  fraterna,  242. 

Hymenoptera,  parasites  of  tsetse  fly 
pupa;,  503. 

Hypoderma  boms,  515-516. 
lineata,  515-516. 

Hypopharynx,  326. 

Hypopus,  339-340. 


Hypopygium,  492. 
Hypostome,  354. 

Iceland,  hydatids,  248,  250. 

Ichneumon  flies,  and  Dermatohiaf 
452. 

Ichthyol,  for  microfilariae,  306;  in 
ointment  for  chiggers,  420. 

Idaho,  spotted  fever,  189. 

Ido,  Y.,  65. 

Ijima,  J.,  252,  253. 

Illinois,     Moniliformis     clarki,     285. 

Immunity,  natural,  19-22;  artificial, 
22-23;  passive,  22;  of  Protozoa 
to  drugs,  34-35;  in  relapsing 
fever,  47;  in  infantile  kala-azar, 
84;  in  oriental  sore,  87;  in 
Rhodesian  sleeping  sickness,  94; 
reactions  among  trypanosomes, 
96-97;  in  malaria,  162-163; 
in  yellow  fever,  71,  72;  in  den- 
gue, 183,  in  phlebotomus  fever, 
185;  in  trichiniasis,  294-295. 

Immunization,  history,  8-9;  in  re- 
lapsing fever,  47;  in  infectious 
jaundice,  68;  in  yellow  fever, 
72;  in  oriental  sore,  88;  against 
trypanosomes,  106. 

Immunology,  development  of,  9. 

Inada,  R.,  65. 

India,  plague  in,  3,  411;  relapsing 
fever,  42,  43,  44;  kala-azar,  77; 
oriental  sore,  85;  amebic  dys- 
entery, 135;  malaria,  147;  ful- 
minant malaria,  163;  Rhino- 
sporidium,  173;  dengue,  182; 
phlebotomus  fever,  184;  Clonor- 
chis  sinensis,  224;  Gastrodis- 
coides hominis,  229;  Tomia  sa- 
ginata  and  dung-eating  habits  of 
cattle,  240;  hookworm  disease, 
262;  use  of  shoes,  265;  land- 
leeches,  319-320;  Rhizoglyphus 
buski,  340;  Ornithodorus  sa- 
vignyi, 361;  bedbugs  and  kala- 
azar,  377;  cat  flea,  416;  chigger, 
420;  malaria-carrying  Anoph- 
eles,  441;     Aedes   calopus,   448; 


552 


INDEX 


Phlehotomus  minutus,  471; 
blackflies,  478;  Chrysomyia 
hezziana,  521. 

Indian  bedbug,  see  Cimex  hemipterus 

Infantile  kala-azar,  82-84;  distribu- 
tion, 82;  transmission,  82-83, 
413,  417;  course  of,  84;  treat- 
ment, 84;   prevention,  84. 

Infantile  paralysis,  195;  and  stable- 
flies,  507. 

Infectious  jaundice,  65;  course  of, 
65-66;  mode  of  infection,  67; 
in  rats,  67-68;  treatment,  68; 
prevention,  68-69. 

Infusoria,  see  Ciliata. 

Insanity,  relation  of  syphilis  to,  53, 
54. 

Insects,  325-330;  general  character- 
istics, 325;  mouthparts,  325- 
327;  general  anatomy,  327-329; 
life  history,  329-330;  classifica- 
tion, 330. 

Intestinal  flukes,  228-230;  life  his- 
tory, 230. 

Intestinal  Protozoa,  115-127;  of 
man  and  animals,  115,  117; 
encystment,  115-116;  specific 
hosts,  116;  geographic  distribu- 
tion, 116;  pathogenic  effects, 
116-117;  prevalence,  116;  bi- 
flagellate  species,  117-118;  mul- 
tiflagellate  species,  118-125,  cili- 
ates,  126,  127;  effects  on  prog- 
ress of  school  children,  266- 
267;  see  also  amebae. 

Intestinal  worms,  entrance  and  exit 
from  host,  201;  effects  on  host, 
201-204;  nutriment  absorbed 
by,  202;  toxic  effects,  202-203; 
infection  of  wounds  made  by, 
203-204;  effects  on  progress  of 
school  children,  266-267;  round 
worms,  270-272;  selection  of 
drug  for  treatment,  270;  search 
for  eggs,  272;  prevention,  266- 
269,  272;  see  also  various  spe- 
cies. 

lodamceba,  129,  132. 


biitschlii,  132,  142. 

Iodine,  for  Trichomonas  infec- 
tions, 122. 

Iodine  or  I.  cysts,  142. 

Ipecac,  and  amebic  dysentery,  137. 

Island  of  Principe,  extermination  of 
sleeping  sickness,  108,  502. 

Ismailia,  reduction  of  malaria,  165. 

Isospora,  in  man,  172,  173. 
hominis,  172. 

Italy,  infantile  kala-azar,  84;  ful- 
minant malaria,  163;  reduction 
of  malaria,  165;  phlebotomus 
fever,  184;  Hymenolepis  nana, 
242;  Moniliformis  monilifor^ 
mis,  284;  Pediculoides,  338; 
breeding  places  of  phlebotomus 
flies,  468. 

Itch,  342,  344-345;  Norwegian,  343; 
treatment,  345-346;  preven- 
tion, 346. 

Itch  mites,  342-346;  description, 
342-343;  life  history,  343-344; 
disease  caused  by,  344-345; 
treatment,  345-346;  preven- 
tion, 346. 

Iturbe,  J.,  217. 

Ixodes,  habits,  356;    characteristics, 
366. 
holocyclus,  and  tick  paralysis,  359, 
pilosus,  and  tick  paralysis,  359. 
ricinus,  367. 

Ixodidaj,  egg-laying  habits,  355 
general  characteristics,  356-357 
important  species,  366-367 
key  to  genera,  366. 

Janicki,  C,  246. 

Janthinosoma   lutzi,    carrier   of   Der- 
matobia,  452,  453 
posticata,  452,  453. 

Japan,  relapsing  fever,  43;  infec- 
tious jaundice,  65,  67;  rat-bite 
fever,  73;  seven-day  fever,  73d; 
kedani,  190;  Schistosoma  jap- 
onicum,  218,  219;  lung  flukes, 
220,  223;  human  liver  flukes, 
224,  225,  227;    Yokagawa  yoka- 


INDEX 


553 


gawa,  228;  Heterophyes  hetero- 
phyes,  228;  Davainea  formos- 
ana,  244;  Diphyllobothrium 
latus,  246;  Diplogonoporus 
grandis,  247;  ,Sparganum  man- 
soni,  252;  Sparganum  prolife- 
rum,  252-253;  Trichostrongylus 
orientalis,  282;  land-leeches, 
319-320;  kedani  mite,  336-337; 
rat  flea,  417;  malaria-carrying 
Anopheles,  441. 

Japanese  flood  fever,  see  Kedani. 

Japanese  seven-day  fever,  73d. 

Java,  malaria  in  children  and  adults, 
162;  hce  and  plague,  399-400; 
Xenopsylla,  417. 

Jenner,  E.,  4,  9. 

Jepps,  M.,  142. 

Jigger,  see  Dermaiophilus  penetrans. 

Jimson  weed,  for  mosquitoes,  456. 

JoHANNSEN,  C.  A.,  339,  474 

Johns,  F.  M.,  9,  149. 

Johnson  (Mrs.),  see  Lawson,  Mary 

Kabure,  relation  to  Schistosoma  ja- 
ponicum,  218. 

Kala-azar,  77-82;  distribution,  77 
transmission,  77-79,  377 
human  cycle  of  parasite,  79 
course  of,  80;  mortahty,  81 
treatment,  81;  prevention,  81- 
82;   see  also  Infantile  kala-azar. 

Kaneko,  R.,  73. 

Kansas,  screw-worm,  521. 

Katajama,  see  Blanfordia. 

Kedani,  168,  169,  186,  190-191. 

Kedani  mite,  see  Leptus  akamushi. 

Keen,  W.  W.,  10. 

Kellogg,  V.  L.,  389. 

Kerosene,  see  Petroleum. 

KiUifish,  natural  enemies  of  mos- 
quitoes, 460-461. 

Kinetonucleus,  see  Parabasal  body. 

King,  A.  F.  A.,  149. 

King,  H.  H.,  482,  487. 

King,  W.  V.,  156. 

King,  W.  W.,  368. 

Kinghorn,  a.,  100. 


Kissing,  and  syphilis,  51;  and  ame- 
bic infections  of  mouth,  146. 

Kissing  bugs,  382. 

Kleine,  F.  K.,  310. 

Knab,  F.,  429,  435,  436,  437,  444, 
447,  451,  453,  458. 

KoBAYASHi,  H.,  226,  227. 

Koch,  R.,  8,  9,  162. 

KoFoiD,  C.  A.,  112,  118,  120,  124, 
132,  134,  141,  206,  381. 

Korea,  lung  flukes,  222;  Clonorchis 
sinensis,  224,  225;  Yokagawa 
yokagawa,  228. 

KORNHAUSER,  S.  J.,  118,  134. 

Kulagin,  N.  M.,  442. 

Labella,  of  mosquitoes,  427. 

Labial  palpi,  325. 

Labium,  325. 

Labrum,  325. 

Labrum-epipharynx,  326. 

Lamhlia,  see  Giardia. 

Lamborn,  W.  a.,  493,  503. 

Land-leeches,  319-321. 

Laning,  R.  H.,  218. 

Larvicides,  457-459. 

Laveran,  a.,  7,  148,  471. 

Laverania  malarioe,  see  Plasmodium 
falciparum. 

Lawson,  Mary  R.,  150. 

Lazear,  J.  W.,  70,  443. 

Leeches,  316-321;  general  anatomy, 
315-316;  importance  as  para- 
sites, 315,  316-317;  intermedi- 
ate hosts  of  trypanosomes,  317; 
in  nose  and  throat,  317-318; 
land-leeches,    319-321. 

Leeuwenhoek,  a.  van,  6,  37,  391. 

Leiper,  R.  T.,  8,  211,  215,  216, 
216b,  217,  219,  224,  228,  230, 
267,  310. 

Leishman,  W.  B.,  7,  43,  74. 

Leishman    bodies,    see    Leishmania. 

Leishmania,  74-92;  discovery,  7,  74; 
transformations  in  insects,  74; 
species,  75,  76;  relationships, 
75;  diseases,  76;  and  kala-azar, 
77-82,  377;    and  mfantile  kala- 


554 


INDEX 


azar,  82-84;    and  oriental  sore, 
84-88,    377-378;     of    uta,    86; 
stage  of  trypanosomes,  95. 
americana,  76,  89;  and  espundia, 

89-92. 
hraziliensis,  see  L.  americana. 
donovani,  discovery,  7,  74;    culti- 
vation,    9,     76,     78;     develop- 
ment   in    bedbugs,    77-78;     in 
Anopheles      punctipennis,      78; 
human   cycle,   79;     distribution 
in  body,  80. 
infantum,  76;    infantile  kala-azar, 

82-84. 
tropica,  76;    in  oriental  sores,  85; 
transmission,  85-86. 
Leishmaniasis,    in    Panama,    74-75; 
origin    from    insect    flagellates, 
75;   see  also  Kala-azar,  Oriental 
Sore  and  Espundia. 
Lemon  juice,  for  land-leeches,  319; 

repellent  for  mosquitoes,  455. 
Leprosy,    spread   by   bedbugs,    379. 
Leptomonas,  see  Herpetomonas. 
Leptospira,  67;    possibly  parasite  of 
dengue  and  phlebotomus  fever, 
182. 
hebdomadis,  73d. 

icterohcemorrhagioe,   discovery,    65; 
description,  66-67 ;  effect  of  sal- 
varsan  on,  68. 
icter aides,  70. 
Leptus,  336;   see  also  Harvest  mites. 
akamushi,   and  kedani,    190,   333. 
americanus,  336. 
autumnalis,  336. 
irritans,  336. 
Leuckart,  R.,  7,  202. 
Leucocytes  or  white  blood  corpus- 
cles, prey  on  parasites,  20. 
Lewis,  T.  R.,  298. 

Lice,  intermediate  hosts  of  Dipylid- 
ium  caninum,  245;  fumigation, 
386,  387-403;  importance,  387; 
general  structure,  388-389;  hu- 
man species,  389;  specificity  of 
action  of  salivary  juice,  393; 
]ice  and  disease,  397-400;    and 


typhus,  8,  378,  397-398;  and 
relapsing  fever  44-46,  378,  398- 
399;  and  trench  fever,  187-188, 
399;  and  bubonic  plague,  399- 
400;  and  syphjlis,  400;  dispersal, 
400;  prevention,  400-403;  con- 
trol in  war,  402-403;  body 
louse,  see  Pediculus  humanus 
corporis;  head  louse,  see  Ped- 
iculus humanus  capitis;  crab- 
louse,  see  Phthirius  pubis. 

Life  histories  of  parasites,  discover- 
ies of,  7. 

Lima,  A.  C,  458. 

Limncea,  host  of  Fasdola  hepatica, 
209;  host  oi  Schistosoma  japoni- 
cum,  219;  occurrence  in  United 
States,  220. 

Limnaiis  nilotica,  316;  in  nose  and 
mouth,  317-318. 

Linguatula  rhinaria,  349-350. 

Linguatulina,  333,  348-351. 

LiNSTow,  O.  F.,  VON,  245. 

LisTON,  W.  G.,  411. 

Liver  abscess,  sequel  of  amebic  dys- 
entery, 134,  137;  in  a  case  of 
myiasis,  527. 

Liver  flukes,  of  sheep,  goats,  etc., 
209-211,  224;  human,  224-228; 
symptoms,  227;  prevention, 
227-228. 

Livingston,  D.,  360. 

Llama,  host  of  Tosnia  saginata,  240. 

Lloyd,  L.,  495,  496. 

Loa  loa,  308-310;  and  Chrysops,  489. 

London,  copra  itch,  340. 

Loess,  A.,  258. 

LoscH,  F.,  7. 

Louse-mite,  see  Pediculoides  veniri- 
cosus. 

Lucilia,  521. 
ccesar,  521. 

Luetin  test,  for  syphilis,  55. 

Lung  flukes,  relation  of  crabs  to, 
8;  220-224;  distribution,  220; 
relation  to  host,  220-221;  life 
history,  211, 221-223;  mode  of  in- 
fection, 223;  prevention,  223-224. 


INDEX 


555 


Lunule,  frontal,  465. 

LuTz,  A.,  217. 

Lymphangitis,  in  filarial  disease, 
305. 

Lynch,  K.  M.,  117,  120,  140. 

Lyon,  H.,  409. 

Lyperosia  irritanSy  see  Hcematobia 
serrata. 

Lysol,  in  prevention  of  filarial  infec- 
tions, 307;  for  chiggers,  420. 

MacAdam,  W.,  135. 

MacConnell,  J.  F.  P.,  7. 

McCuLLOCH,  Miss  I.,  112,  381. 

Macfie,  J.  W.  Scott,  98,  507. 

MacGregor,  W.,  7. 

Mackie,  F.  p.,  81. 

McNauqhton,  J.  G.,  306. 

MacNeal,  W.  J.,  9,  10. 

Macronucleus,  28. 

Macrostoma,  see  Chilomastix. 

Madagascar,  Triatoma  ruhrofasciata, 
381;  surra,  487. 

Maggots,  in  espundia  sores,  90;  and 
myiasis,  509-528;  characteris- 
tics, 509-510;  blood-sucking, 
511-513;  under  skin,  513-519; 
in  wounds  and  natural  cavities 
of  body,  519-523;  in  intestine, 
523-528;  in  urinary  passages, 
528;  resistance  to  reagents,  522, 
526-527. 

Magnesium  sulphate,  in  treatment 
of  amebic  dysentery,  139. 

Malaria,  in  Panama,  2;  importance 
of,  5,  147-148;  relation  of  mos- 
quitoes to,  7,  149,  157-159; 
147-167;  prevalence  of,  148; 
history,  148-149;  parasites  of, 
149-150;  occurrence  of  attacks 
of  ague,  153;  quotidian,  153; 
numbers  of  parasites,  153; 
over-wintering,  156;  benign 
vs.  malignant,  156;  propaga- 
tion, 157-159;  latent,  158; 
effect  of  weakening  of  host, 
158-159;  course  of,  tertian  and 
quartan,     159-161;     aestivo-au- 


tumnal,  161;  immunity,  162- 
163;  tropical  vs.  subtropical, 
162;  carriers,  162,  165,  438- 
443;  fulminant,  163;  treat- 
ment, 163-164;  prevention, 
164-167;  number  of  mos- 
quitoes necessary  to  propagate, 
165. 

Malarial  parasites,  see  Plasmodium, 

Malay  bug,  see  Triatoma  ruhrofas- 
ciata. 

Malay  States,  kedani  or  pseudo- 
typhus,  190;  Echinostomum, 
228;  malaria-carrying  Anop/ieZes, 
441;   habits  of  Anopheles,  441. 

Malcoeur,  254. 

Mai  de  boca,  cause  of,  73a-73b. 

Mai  d'estomac,  254. 

Male  fern,  for  tapeworms,  237;  for 
hookworms,  264;  for  pin  worms, 
279. 

Malloch,  J.  R.,  480. 

Mallophaga,  Rickettsia  in,  185;  com- 
pared with  Anoplura,  388. 

Malmsten,  p.  H.,  7,  37. 

Malpighian  tubules,  328. 

Malta,  phlebotomus  flies,  468,  470, 
471. 

Manaos,  reduction  of  yellow  fever, 
70,  72. 

Manchuria,  plague,  413. 

Mandibles,  of  insects,  325. 

Mange,  342. 

Mangrove  fly,  see  Chrysops. 

Manila,  Balantidium  infections,  127; 
amebic  dysentery,  130;  Echino- 
stomum ilocanum,  229;  Tcenia 
philippina,  245. 

Manson,  Sir  P.,  7,  47,  80,  162,  298, 
301,  305,  309,  322,  449. 

Mansonia,  habits  of  larvse,  431; 
host  of  Filaria,  450. 

Manure,  treatment  to  prevent  fly- 
breeding,  508. 

Marett,  p.  J.,  468. 

Margaropus  annulatus,  12;  life  his- 
tory, 356,  366;  extermination, 
368. 


656 


INDEX 


Marlatt,  C.  L.,  373,  375,  376. 

Marmot,  host  of  Moniliformis 
moniliformis,  284;  and  plague 
in  Manchuria,  413. 

Marriage,  syphiHs  and,  60-61. 

Masterman,  E.  W.  G.,  317,  318. 

Mastigamaeba,  35. 

Mastigophora,  see  Flagellata. 

Mauritius,  Holothyrus  coccinella, 
341;  trypanosomes  in  Tria- 
toma  ruhrofasdata,  381. 

Maxilla,  325. 

Maxillary  palpi,  325. 

Mayflies,  life  history,  329. 

Mayne,  M.  B.,  156. 

Mealworm,  intermediate  host  of  Hy- 
menolepis  diminuta,  244. 

Measles,  human,  169,  193;  beef, 
240;  pork,  241. 

Meat,  fitness  for  food  when  dis- 
eased, 296-297. 

Meat  inspection,  286;  relation  to 
trichiniasis,  295-296. 

Medical  entomology,  beginning  of, 
7;  summary,  322-323. 

Mediterranean  countries,  infantile 
kala-azar,  82;  oriental  sore,  84, 
85;  dengue,  182;  phlebotomus 
fever,  184;  Schistosoma  hoema- 
tobium,  213;  Limnatis  nilotica, 
317;  phlebotomus  flies,  470. 

Megarhinus,  437. 

Melania,  host  of  lung  fluke,  221;  not 
of  Clonorchis  sinensis,  226;  of 
Yokagawa,  228. 
libertina,  and  Paragonimus  ringeri, 
221;  and  Clonorchis  sinensis, 
226;  and  Yokagawa,  228. 

Melanolestes,  382. 
picipes,  382. 

Melittophagus  meridionalis,  and 
tsetse  flies,  503. 

Melophagus,  Rickettsia  in,  185. 

Membranelles,  30. 

Mercurial  ointment,  for  crab  hce, 
401. 

Mercuric  chloride  (corrosive  subli- 
mate), for  syphilis,  56;   for  rat- 


bite  fever,  73a;  for  guinea- 
worm,  314;  for  destroying  flea 
eggs,  421;  to  remove  Dermato- 
hia  from  skin,  515. 

Merida,  yellow  fever  in,  70. 

Mesozoa,  27. 

Metagonimiis,  see  Yokagawa. 

Metamorphoses,  of  insects,  329. 

Metastrongylus  apri,  200. 

Metazoa  vs.  Protozoa,  26-27. 

Methylene  blue,  for  Trichomonas  in- 
fections, 121;  for  Balantidium 
infections,  127. 

Mexico,  relapsing  fever,  46;  amebic 
dysentery,  130,  136;  tlal- 
sahuate,  335;  Ornithodorus, 
361,  365;  Otiobius  megnini,  365; 
distribution  of  lice,  394;  hce 
and  typhus,  186,  396,  397. 

Miana  tick  or  bug,  see  Argus  persi- 
cus. 

Mice,  and  infantile  kala-azar,  82; 
hosts  of  human  intestinal  Pro- 
tozoa, 116;  Giardia  of,  125; 
spread  of  Sarcosporidia  among, 
175;  Sarcocystis  muris,  176;  and 
kedani  mite,  190;  experimental 
infection  with  Schistosoma, 
217,  219;  Hymenolepis  nana 
and  diminuta,  242-244;  and 
bedbugs,  375;  Moniliformis 
moniliformis,  284;  trichina, 
288,  296;  occasional  hosts  of 
Pulex  irritans,  414. 

Microfilaria,   discovery,  7,  29^300; 
periodicity,  301;   effect  of  drugs 
on,  306. 
bancrofti,     299-300;      periodicity, 
301;    effect  of  drugs  on,   306; 
comparison  with  mf.  loa,  309. 
juncea,  308. 
loa,  309. 
perstans,  308. 
volvulus,  311. 

Micronucleus,  28. 

Microtus  montebelli,  and  Japanese 
seven-day  fever,  73d;  and  ke- 
dani, 190,  336. 


INDEX 


557 


Mice,  and  Giardia,  125. 

MiDDLETON,  W.  S.,  144. 

Midges,  see  Chironomidae. 

MiGLIANO,  L.,  73c. 

Miller's  itch,  caused  by  Pediculoides, 
338. 

"Millions,"  natural  enemy  of  mos- 
quitoes, 460-461. 

Mimm's  culicide,  456. 

Minas  Geraes,  Triatoma  megista,  380. 

Miner's  itch,  see  Hookworm. 

Mines,  hookworm  in,  262,  265. 

Miracidium,  209. 

Mites,  and  kedani,  190;  general 
account,  331-332;  life  history, 
332;  parasitism,  332-333;  fami- 
lies containing  parasites,  333; 
toxic  effects  of  salivary  juices, 
337;    see   also   various   species. 

MiTZMAiN,  M.  B.,  see  Mayne,  M.  B. 

MiYAiRi,  K.,  218,  219,  222. 

Moco,  host  of  Triatoma  chagasi,  381. 

Mongols,  possibly  result  of  syphihs, 
53. 

Moniliformis  moniliformis,  284-286. 
clarki,  285. 

Monkeys,  for  experimentation,  10; 
relapsing  fever,  43,  47;  and  in- 
fantile kala-azar,  82;  and  es- 
pundia,  89;  susceptible  to  Schis- 
tosoma infections,  216a;  Tri- 
churis  trichiura,  277;  hosts  of 
Ternidens  deminutus,  283;  (Eso- 
phagostomum  apiostomum,  283; 
probable  host  of  (Esophagos- 
tomun  stephanostomum  thomasi, 
283;  and  plague,  413. 

Montana,  spotted  fever,  188,  189; 
Porocephalus  in  man,  351. 

Morales,  R.,  451. 

Moscow,  transmission  of  relapsing 
fever,  378;  habits  of  Anoph- 
eles, 442. 

Mosquitoes,  and  espundia,  92;  and 
Oroya  fever,  181;  mouthparts, 
327,  426-427;  fumigation,  386, 
456;  424-462;  importance,  424; 
general  structure,  425-428;  dis- 


eases carried  by,  424;  relation- 
ships, 425;  sexes  distinguished, 
426;  life  history,  428-433;  hab- 
its of  adults,  433-434;  habitats, 
434;  migration,  434-435;  time 
of  activity,  435-436;  food  hab- 
its, 436;  hibernation,  436; 
length  of  life,  436-437;  clas- 
sification, 437;  effect  of  bites, 
453;  remedies  for  bites,  454- 
455;  personal  protection,  455- 
456;  ehmination  and  exclusion 
from  buildings,  456-457;  lar- 
vicides,  457-459;  prevention 
of  breeding,  459;  natural  ene- 
mies, 459-462. 
and  malaria,  discovery,  7;  develop- 
ment of  Plasmodium  falciparum 
in,  154-156;  malaria  carriers, 
157-159,  438-441;  number  neces- 
sary to  propagate  malaria,  165; 
habits  of  Anopheles,  441-443; 
and  yellow  fever,  discovery,  7,  443; 
transmitting  species,  443-448; 
and  Filaria,  discovery,  7,  298, 
449;  development  of  Filaria 
bancrofti  in,  301-303,  450-451, 
as  transmitting  species,  450- 
451; 
and  dengue,  discovery,  8,  448; 
183;  transmitting  species,  448- 
449; 
and  Dermatobia,  451-453,  514; 
objections  to  mosquito  trans- 
mission theory,  452;  transmit- 
ting species,  453. 

Mosquito-worm,  451. 

Mouchet,  R.,  351. 

Mould,  cause  of  kedani,  192. 

Mouth,  spirochsBtes  in,  70;  Tri- 
chomonas in,  119;  amebse  in, 
142-146B. 

Mouth  ameba,  see  Endamoeha  gin- 
givalis. 

Mouthparts  of  insects,  325-327. 

Mule,  host  of  Dermatobia,  513. 

Murray,  C.  H.,  371,  372,  374,  375. 

Musca  domestica,   changed  attitude 


558 


INDEX 


towards,  3;  stable-flies  mistaken 
for,  504;  breeds  in  manure,  508; 
and  intestinal  myiasis,  527. 

Muscidae,  includes  tsetse  flies,  491; 
stable-flies,  504;  other  blood- 
suckers, 506;  captured  by  Der- 
matobia,  514;  screw-worm,  519; 
other  species  causing  myiasis  of 
wounds,  521. 

MUSGRAVE,  W.  E.,  221. 

MuTO,  M.,  226. 

Myiasis,  509-528;  definition,  509; 
flies  causing,  509;  classification, 
510;  by  blood-sucking  maggots, 
511-513;  of  skin,  513-519;  of 
wounds  and  natural  cavities  of 
body,  519-523;  of  intestine, 
523-528;  of  urinary  passages, 
528. 

Myoneme,  31. 

Myriapoda,  324-325. 

Nagana,  108,  497. 

Nagayo,  M.,  192,  337. 

Nakagawa,  K.,  8,  221,  222,  223. 

Naphthahne,  for  intestinal  fluke  in- 
fections, 230;  for  body  lice,  401, 
402;  to  eliminate  fleas,  421, 
422-423. 

Nasal  polypus,  173-174. 

Natal,  hookworm  quarantine,  268; 
Cordylobia  anthropophaga,  518. 

NCI,  for  Hce,  402. 

Nebraska,  Tcenia  confusa,  245. 

Necator  americanus,  distribution, 
255;  description,  255-257;  see 
also  Hookworms. 

Negri  bodies,  170,  191-193. 

Negroes,  syphilis  among,  51;  im- 
munity to  malaria,  163. 

Neiva,  a.,  381,  452;   514. 

Nematoda,  198;  intestinal,  270-272, 
282;    see   also   various   species. 

Nematomorpha,  199. 

Nemathelminthes,  198-199;  intes- 
tinal forms,  270-272;  see  also 
various  species. 

Nemertinea,  198. 


Neosalvarsan,  for  syphilis,  57;  to 
prevent  trypanosome  infection, 
107. 

Nephridia,  199. 

Neurorydes   hydrophohice,    170,    191- 

193. 
New  Jersey,  ecologic  groups  of  mos- 
quitoes, 434;  migrations  of  salt 
marsh  mosquitoes,  435;  control 
of  salt  marsh  mosquitoes,  459- 
460. 

New  Orleans,  plague  in,  2,  411; 
yellow  fever,  69-70. 

Newstead,  R.,  470,  471. 

Newt,  natural  enemy  of  mosquitoes, 
461. 

New  York,  amebse  in  school  chil- 
dren, 143;  invasion  by  mosqui- 
toes, 435. 

Nichols,  H.  J.,  54. 

NicoLL,  W.,  267. 

NicoLLE,  C.  N.,  8,  44,  397,  398,  399. 

Nigeria,  sleeping  sickness,  98,  102,. 
104;  transmission  of  sleeping 
sickness,  500. 

Nighthawk,  natural  enemy  of  mos- 
quitoes, 462. 

Night-soil,  use  in  oriental  countries, 
227-228,  267. 

Nimetti,  482. 

Nit,  391. 

NoGUCHi,  H.,  9,  67,  70,  71,  72,  182. 

Noma,  cause  of,  73a;  treatment, 
73b. 

North  America,  infectious  jaundice, 
65;  tick  paralysis,  358;  Der- 
macentor  variabilis,  367;  Red- 
uviidae,  382;  typhus,  186,  398; 
mosquito  scourge,  424;  mala- 
ria-carrying Anopheles,  439; 
blackflies,  481. 

No-see-um,  474. 

Notoedres  cati,  343. 

Notophthalmus  iorosus,  natural  en- 
emy of  mosquitoes,  461. 

NovY,  F.  G.,  9,  23-25. 

NuTTALL,  G.  H.  F.,  34,  395. 

Nymph,  329,  332. 


INDEX 


559 


Obermeier,  O.,  7,  43. 

O'Connor,  F.  W.,  118,  121. 

Odocoileus  columbianus,  and  Pulex 
irritans,  414. 

(Estridae,  characteristics  of  larvse, 
509;  and  intestinal  myiasis,  524. 

(Estrus  ovis,   and  myiasis,   522-523. 

CEsophagoslomum    apiostomum,    283. 
brumpli,  see  (E.  apiostomum. 
stephanostomum  thomxisi,  283* 

Ogata,  M.,  192. 

Oil,  poured  in  ears  to  remove  Olio- 
bins  megnini,  366;  for  removal 
of  ticks,  367;  film  to  destroy 
mosquito  larva),  458,  460;  film 
to  trap  tabanids,  489-490. 

Okuda,  K.,  73. 

Onchocerca  volvulus,  310-311. 
ccBcutiens,  311. 

Ontario,  blackflies,  479,  481,  482. 

Onychophora,  324. 

Opilaggo,  255. 

Opisthorchis  felineu^,  226. 
noverca,  225. 
pseudofelineus,  225. 

Opsonin,  20. 

Oregon,  trichina,  292;  tick  paralysis, 
358-359;  Dermacentor  occiden- 
talism 363;  Notophthalmus  toro- 
sus  and  mosquitoes,  461;  Cul- 
icoides,  476;  blackflies,  481. 

Oregon  State  Board  of  Health,  corre- 
spondence concerning  venereal 
diseases,  59. 

Organelles,  29-32. 

Oriental  sore,  84-88;  distribution, 
84-85;  transmission,  85-86, 
377-378,  477,  488;  susceptible 
animals,  86;  course  of,  86-88; 
treatment,    88;    prevention,   88. 

Ornithodorus,    effect    of    bites,    361, 
364. 
coriaceus,    effect    of    bites,    364- 

365. 
megnini,  see  Otiobius  megnini. 
moubata    and    relapsing     fever, 
43-44,360-361;  control,  369. 
savignyi,  and  relapsing  fever,  44, 


361;  control,  369. 
talaje,    and    relapsing    fever,    46, 
361;    habits,  361;    control,  369. 
tholosani,  and  relapsing  fever,  44, 

361. 
turicata,  and  relapsing  fever,  46, 
361;    severity  of  attacks,  361; 
control,  369. 

Oroya  fever,  168,  176-181;  history, 
176;  distribution,  176;  con- 
fusion with  other  diseases,  177; 
course  of,  179;  parasite  of,  179- 
181;  transmission,  181,  360. 

Orthetrum  chrysostigma,  preys  on 
tsetse  flies,  503. 

Orthorrhapha,  pupse,  465,  466;  and 
myiasis,  509. 

OsLER,  Sir  W.,  49. 

OsuMi,  S.,  73. 

Otiobius  megnini,   365-366. 

Owl  midges,  see  Phlebotomus  flies. 

Oxyuris  vermicularis,  nutriment  ab- 
sorbed, 202;  277-279. 

Pajaroello,  364. 

Palestine,  leeches  in  nose  and  mouth, 
317-318. 

Palpi,  of  insects,  325;  of  acarina, 
331. 

Panama,  French  failure  and  Ameri- 
can success,  2;  yellow  fever  dur- 
ing French  operations,  71; 
Leishmania  sores,  74-75,  488; 
malaria  and  the  Canal,  149; 
non-malarial  Anopheles,  158; 
reduction  of  malaria,  166; 
malaria-proof  houses,  166;  re- 
duction of  yellow  fever,  71; 
dengue,  182,  oil  films  for  mos- 
quitoes, 459. 

Pangonia,  485,  486. 

Papataci  fever,  see  Phlebotomus 
fever. 

Parabasal  body,  29-30. 

Paraform,  larvicide,  459. 

Paragonimus,  220-224;  see  also  Lung 
flukes. 
keUicotti,  220,  223. 


660 


INDEX 


ringeri,  220-224. 
westermani,  see  P.  ringeri. 

Paraguay,  rattlesnakes  and  espun- 
dia,  92,  471. 

Paralysis,  general,  result  of  syphilis, 
53,  54;  from  tick  bites,  358-359. 

Paramcecium,  old  age,  33. 

Paramphistomum  cervi,  229. 

Paraplasma  fiavigenum,  and  yellow 
fever,  184. 

Parasites,  discoveries  of,  7;  life  his- 
tories discovered,  8;  definition, 
12;  kinds  of,  12-13;  effects  of 
parasitism  on,  14;  effects  on 
hosts,  15-17;  modes  of  infec- 
tion and  transmission,  17;  geo- 
graphic distribution,  18-19; 
effects  of  temperature,  19;  im- 
munity to,  19-22;  introduction 
to  virgin  territory,  20;  relation 
to  intermediate  and  to  final 
hosts,  450-451. 

Parasitic  diseases,  history  of  treat- 
ment of,  8. 

Parasitidae,  333,  341. 

Parasitism,  degrees  of,  12;  effects  on 
parasites,  14;  origin  among 
mites,  332-333. 

Parasitology,  importance  of,  5;  his- 
tory of,  6-11. 

Paratyphoid,  confused  with  Oroya 
fever,  178. 

Paris,  syphilis  in,  50. 

Pasteur,  L.,  7,  9,  20. 

Patagonia,  Filaria  hancrofti,  299. 

Patton,  W.  S.,  77,  377,  416;  521. 

Peacock,  A.  D.,  7. 

Pediculoides  ventricosus,  337-339. 

Pediculus,  hosts,   389,   Rickettsia  in, 
185-187. 
capitis,  see  P.  humanus  capitis, 
corporis,  see  P.  humanus  corporis, 
humanus    capitis,    389,    compared 
with  corporis,  389-390,  394-395; 
394-396;      habitat,     395;      fife 
history,    395;    effects    of    bites, 
395-396;    and  typhus,  397;  and 
relapsing  fever,  398;  and  plague. 


399-400;  dispersal,  400;  reme- 
dies, 401. 
humanus  corporis,  389-394;  com- 
pared with  capitis,  389-390, 
394-395;  and  disease,  390,  397- 
400;  habitat,  390;  life  history, 
391-393;  habits,  393-394;  ef- 
fects of  bites,  394;  and  typhus, 
397-398,  186;  and  relapsing 
fe.ver,  398-399,  44-46;  and 
trench  fever,  399,  187-188;  and 
plague,  399-400;  dispersal, 
400;  eradication,  401-403. 
vestimcnti    see    humanus   corporis. 

Pedipalpi,  331. 

Pellagra,  and  blackflies,  483. 

Pelletririne,  for  tapeworm  infections, 
237. 

Pennyroyal,  oil  of,  repellent  for  fleas, 
422;  for  mosquitoes,  455. 

Penschke,  420. 

Peppermint,  oil  of,  repellent  for 
mosquitoes,  455. 

Pericoma  ioums.vilIensis,  466. 

Peripatus,  324. 

Persia,  African  relapsing  fever,  44; 
oriental  sore,  85,  86;  Ornitho- 
dorus  tholosani,  361;  Argas  persi- 
cus,  364. 

Persian  insect  powder,  see  Pyre- 
thrum  insect  powder. 

Peru  uta,  86;  oriental  sore,  87; 
Trichomonas  pathogenic,  121; 
Oroya  fever,  176,  181,  472;  lung 
fluke,  224;  breeding  places  of 
phlebotomus  flies,  468;  Phle- 
hotomus  verrucarum,  472,  473. 

Petroleum,  for  removal  of  ticks,  367; 
for  bugs,  383;  emulsion  for  head 
lice,  401;  for  body  lice,  401, 
402;  for  chigger  wounds,  420; 
for  mosquitoes,  457;  for  mos- 
quito  larvae,  458. 

Phalangomyia    dehilis,    and    Oroya 

fever,  181. 
Philcemon,  320. 

Philippine  Islands,  dengue,  182; 
kedani,    190;     Schistosoma  jap- 


INDEX 


561 


anicum,  218;  lung  flukes,  220, 
221;  human  liver  flukes,  224; 
Eckinostomum  ilocanum,  228; 
TcBTiia  solium,  241;  (Esophagosto- 
mum  apiostomum,  283;  Anoph- 
eles ludlowi,  habits,  442;  Miisca 
domestica  and  intestinal  myiasis, 
527. 

Phinotas  oil,  for  blackflies,  483. 

Phlehotomus,  and  oriental  sore,  86, 
471;  and  Oroya  fever,  181,  472- 
473;  and  phlehotomus  fever, 
184-185,  470-471;  463;  466- 
473;  general  description,  466- 
468;  life  history,  468-470;  and 
diseases,  470-473;  control,  473. 
pernidosus,       and      phlehotomus 

fever,  470. 
minutus,  and  oriental  sore,  86,  471; 
and    phlehotomus    fever,    470; 
hahits,  471;   description,  472. 
minutus,  var.  ajricanus,  and  orien- 
tal sore,  86,  471. 
papatasii,  and  phlehotomus  fever, 
184,  185,  470;  life  history,  469; 
description,  hahits,  etc.,  470-471. 
verrucarum,  and  Oroya  fever  and 
verruga    peruviana,    181,    472- 
473. 

Phlehotomus  fever,  parasites  of, 
182;  184-185. 

Phthirius,  hosts,  389. 
inguinalis,  see  P.  pubis, 
pubis,    389,    396-397;     dispersal, 
400;  remedies,  401. 

Physaloptera  mordens,  282. 

Physopsis  africana  intermediate 
host  of  Schistosoma  hoematobium 
in  South  Africa,  216. 

Pigeon,  Argas  reflexus,  364. 

Pin  worm,  see  Oxyuris  vermicvlaris. 

Piophila  casei,  and  intestinal  myi- 
asis, 526,  527. 

Piroplasmata,  27,  168;  Bartonella  a 
member  of,  180-181;  and 
spotted  fever,  168;  and  kedani, 
190-191;  transmission  by  ticks, 
168,  181,  360. 


Pito  bug,  382. 

Plague,  in  Europe,  2,  411;    in  Uni- 
ted States,  2,  411;   in  India,  3, 
411;    and    bedbugs,    378;    and 
lice,  399-400;    and  fleas,  410- 
413;  and  rats,  411. 
Planorbis,     occurrence     in     United 
States,  220. 
boissyi,      intermediate      host      of 
Schistosoma  mansoni  in  Egypt, 
215,  216,  217. 
gvxidelupensis,    intermediate    host 
of  Schistosoma  mansoni  in  Ven- 
ezuela, 217. 
olivaceus,     intermediate     host    of 
Schistosoma  munsoni  in  Brazil, 
217. 

Plasmodium,  discovery,  7;  cultiva- 
tion, 9;  35;  149-159;  species, 
149-150;  life  history,  human 
cycle,  150-154;  relation  to  red 
blood  corpuscles,  150-151;  mos- 
quito cycle,  154-156;  effects  of 
temperature  on  development  in 
mosquito,  156. 
falciparum,  150-156;  life  history, 
human  cycle,  150-154;  clogging 
of  capillaries,  152;  sporulation, 
152-153;  numbers  in  blood,  153; 
crescents,  154;  mosquito  cycle, 
154-156;  resistance  to  low  tem- 
peratures, 156. 
malaricB,  150;  description,  157. 
vivax,  150;  resistance  to  low  tem- 
peratures, 156;  description, 
156. 

Plate,  J.  T.,  118,  134. 

Platyhelminthes,  196-198. 

Plenciz,  M.  a.,  6. 

Plerocercoid,  nature  of,  235. 

Pliny,  372. 

Pohomyehtis,  acute,  anterior,  see 
Infantile  paralysis. 

Pork,  measly,  241;  trichina  in,  286, 
287,  292;  killing  of  trichina  in, 
295;  inspection,  295-296;  fit- 
ness for  food,  296-297. 

Pork  tapeworm,  see  Tcenia  solium. 


562 


INDEX 


Porocephalus  armillatus,  350-351. 
crotali,  351. 
moniliformis,  351. 

PoRTCHiNSKY,  I.  A.,  487,  489,  490. 

Porter,  A.,  123. 

Porto  Rico,  hookworm  disease,  262; 
unsanitary  conditions,  266. 

Portuguese  Sleeping  Sickness  Com- 
mission, extermination  of  sleep- 
ing sickness  on  Island  of  Prin- 
«      cipe,  108;    eradication  of  tsetse 
flies,  502. 

Potamon  dehaanii,  intermediate  host 
of  lung  flukes,  222. 
ohtusipes,    intermediate    host    of 
lung  fluke,  222. 

Potassium  cyanide,  for  hydrocyanic 
acid  fumigation,  384. 

Potassium  permanganate,  for  trop- 
ical ulcer,  73c. 

Potassium  sulphide,  to  destroy  fleas, 
422. 

Precipitins,  21. 

Price,  J.  D.,  377. 

Priestley,  H.,  73d. 

Privies,  lack  of,  in  warm  countries, 
266. 

Procercoids,  246-247. 

Proglottid,  232. 

Prostitution,  and  syphilis,  61; 
municipal  control  of,  61-62. 

Protista,  27. 

Protozoa,  vs.  Metazoa,  26-27;  vs. 
bacteria,  27;  structure,  28-29; 
organelles,  29-32;  nutrition,  32; 
reproduction,  32-34;  life  cycle, 
33-34;  immunity  to  drugs,  34- 
35;  classification,  35-36;  im- 
portance, 37;   discovery,  37. 

Protozoology,  importance  of,  37. 

Prowazekella,  118. 

Prowazek's  bodies,  193. 

Pseudopodia,  29. 

Pseudotyphus,  190. 

Psorophora,  larvae  prey  on  Janthino- 
soma  larvae,  453. 

Psychodidae,  466. 

Ptilinium,  465. 


Pulex  irritans,  jumping  power,  405: 
identification,  408;  egg-laying 
habits,  408;  life  cycle,  410;  and 
plague,  412;  and  infantile  kala- 
azar,  413;  and  Dipylidium  can- 
inum,  414;  habits,  etc.,  414- 
415. 

Puhcidae,  407. 

Punkies,  see  Chironomidse. 

Puparium,  465. 

Pygidium,  404. 

Pygiopsylla  ahaloe,  417. 

Pyorrhea,  142-146b  ;  importance, 
142;  relation  of  amebae  to,  144- 
146;  relation  of  bacteria  to, 
145;  prevention  and  treat- 
ment, 146a-146b. 

Pyrethrum  insect  powder,  for  ticks, 
369;  for  mosquitoes,  456. 

Python,  host  of  Porocephalus,  350, 
351. 

Quack  doctors,  4;  and  syphilis,  56. 
Queensland,  hookworm  disease,  262. 
Quinine,   discovery  and  history,   8; 

for  malaria,  163-164,  167. 
Quininization,     and    prevention    of 

malaria,  165,  166. 
QuiROs,  D.,  419,  420. 

Rabbits,  Eimeria  stiedoB  of,  in  man, 
172;  susceptible  to  trichina, 
288;  Linguatula  rhinaria, 
349;  and  bedbugs,  375;  Echid- 
nophaga  gallinacea,  420. 

Rabies,  169;  parasite  of,  170,  191- 
193. 

Ransom,  B.  H.,  238,  243,  274,  275, 
286,  287,  292,  294,  295. 

Rasahus,  382. 

Rat-bite  fever,  73-73a. 

Rats,  relapsing  fever  immunization, 
47;  reservoir  of  infectious  jaun- 
dice, 67-68;  and  rat-bite  fever, 
73;  Giardia  of,  125;  and  in- 
fantile kala-azar,  82;  devel- 
opment of  Trypanosoma  rhod- 
esiense  in,  97;    hosts  of  human 


INDEX 


563 


intestinal  Protozoa,  116;  and 
amebic  dysentery,  140;  and 
Hymenolepis  nana,  242-244; 
Hijmenolepis  diminuta,  244; 
development  of  Ascaris  in, 
274-275;  Moniliformis  mon- 
iliformis, 284;  relation  to  tri- 
chiniasis,  287,  288,  296;  and 
bedbugs,  375;  occasional  hosts 
of  Pvlex  irritans,  414;  fleas, 
417-418;  Echidnophaga  galli- 
nacea,  420. 

Rattlesnakes,  Porocephalus  crotali, 
351. 

Redbugs,  see  Harvest  mites. 

Redi,  F.,  6. 

Redia,  209,  211. 

Red  spider,  340. 

Reduviidse,  379. 

Reduirius,  382. 

Reed,  W.,  70,  443. 

Relapsing  fever,  42-48;  distribution, 
42;  spirochaetes  of,  42,  46;  trans- 
mission, 43-46,  378,  398-399; 
nature  of,  46-47;  mortality,  47; 
treatment,  47;  prevention, 
47-48;  development  in  lice, 
399. 

Repellents,  for  fleas,  423;  for  mos- 
quitoes, 455;  for  phlebotomus 
flies,  473;  for  chironomids,  477; 
for  tabanids,  489;  for  tsetse  flies, 
501. 

Reptiles,  reservoirs  of  Leishmanian 
diseases,  471;  fed  on  by  tsetse 
flies,  494. 

Reunion,  trypanosomes  in  Triaioma 
rybrofasdata,  381. 

Rhinosporidium,  168;   173-174. 
kinealyi,  173.. 

Rhipicephalus,  366. 

Rhizoglyphus  parasiticus,  340. 

Rhizopoda,  see  Sarcodina. 

Rhodesia,  sleeping  sickness,  94. 

Rhodnius  prolixus,  382. 

Rhynchoprion,     see    Dermatophilus. 

Rhynchota,  see  Hemiptera. 

RiCKETTS,  H.  T.,  8,  186,  188,  397. 


Rickettsia-hke  organisms,  168,  169, 
170,185-191;  194.    ' 

Rickettsia,  181;    in  insects,  185-186; 
in  human  diseases,  186;   191. 
pediculi,  in  lice,  187. 
prowazeki,  and  typhus,  186-187. 
quintana,  and  trench  fever,  187-188. 

RiDEWOOD,  W.  G.,  409. 

Rigg's  disease,  see  Pyorrhea. 

Riley,  W.  V.,  339,  474. 

RiNCONES,  G.,  451-452. 

Rio  de  Janeiro,  reduction  of  yellow 
fever,  70,  72;  Triatoma  vittin 
ceps,    381. 

Robertson,  Miss,  99. 

ROBLES,  R.,  311. 

ROCHA-LIMA,  H.,  186. 

Rockefeller,  J.  D.,  268. 

Rockefeller  Institute,  10,  72,  105. 

Rocky  Mountain  spotted  fever,  see 
Spotted  fever. 

Rodents,  hosts  of  Trypanosoma 
cruzi,  112,  114;  and  spotted 
fever,  189,  369;  susceptible  to 
Schistosoma  infections,  216a; 
hosts  of  immature  stages  of 
Dermacentor  vemistus,  362-363; 
and  Triatoma,  380-381;  plague 
transmitted  by  lice,  399;  hosts 
of  Cordylobia  anthropophaga,  518. 

Rogers,  L.,  8,  9,  81,  377. 

Rosen,  F.,  246. 

Rosen Au,  M.  J.,  48,  507. 

Ross,  Sir  R.,  7,  147,  148,  149,  156, 
158,  164,  165,  449,  457. 

RouBAUD,  E.,  156,  459  471,  512,  517. 

Rougets,  336. 

Roundworms,  see  Nemathelminthes. 

Russia,  relapsing  fever,  43,  45; 
Diphyllohothrium  latus,  246; 
Gigantorynchus.  hirudinaceus  in 
man,  284;  typhus,  398;  Gas- 
trophilus  hoemorrhoidalis  in 
man,  516;  Wohlfartia  magni- 
jica,  521-522. 

Sabethini,  437. 

Sahcylic  acid,  in  ointment  for  chig- 


664 


INDEX 


gers,  420. 

Salt,  enema  for  amebic  dysentery, 
138;  to  destroy  hookworm 
larvae,  267. 

Salt  water,  for  myiasis  of  nose,  ears, 
etc.,  523. 

Salvarsan,  discovery,  8,  49;  for  re- 
lapsing fever,  47;  for  syphilis, 
56-57;  for  yaws,  64;  for  infec- 
tious jaundice,  68;  for  rat-bite 
fever,  73a;  for  Vincent's  angina 
and  noma,  73b;  for  tropical 
ulcer,  73c;  for  trypanosomes, 
105,  107;  for  Balantidium  in- 
fections, 127. 

Salvarsan  copper,  to  prevent  tryp- 
anosome  infections,  107. 

Salzman,  F.,  294. 

Sambon,  L.  W.,  350,  351,  451,  452, 
453. 

Samoa,  periodicity  of  Filaria  ban- 
crofti,  301. 

Sand  flea,  see  Dermatophilus  pene- 
trans. 

Sandflies,  see  Phlebotomus  flies. 

San  Francisco,  plague  in,  2;  anti-rat 
campaign,  411. 

Sanitation,  and  syphilis,  61;  and 
prevention  of  amebic  dysentery, 
139;  relation  to  intestinal 
parasites,  265-269;  effect  on 
school  children's  progress,  266- 
267;  necessity  for  practical 
demonstrations,  268-269. 

Santonin,  for  intestinal  fluke  infec- 
tions, 230;  for  Ascaris  infec- 
tions, 276. 

Sao  Paulo,  Triatoma  sordida,  381; 
Dermatohia    transmitters,     453. 

Sarcocystin,  toxin  from  Sarcospor- 
idia  spores,,  175. 

Sarcocystis  muris,  sexual  phenomena, 
176. 
tenella  huhalis,  in  Indian  buffaloes, 
176. 

Sarcodina,  pseudopodia  in,  29,  36, 
129. 

Sarcophaga  fuscicauda  and  intestinal 


myiasis,  526. 
magnifica,     see     Wohlfartia    mag- 
nifica. 
Sarcophagidae,  521. 
Sarcopsyllidae,  407,  418,  420. 
Sarcoptes,  342-346. 
scahid,  342-346. 
scabiei  crustosce,  343,  345. 
Sarcoptidse,  333,  342. 
Sarcosporidia,  168,  174-176;  in  man, 

176. 
Savarelli,  184. 
Scabies,  342. 
Scarlet  fever,  169,  191. 
ScHAUDiNN,  F.,  7,  49,  428. 
Schistosoma,   discovery,   7;     life  his- 
tory discovered,  8,  213;  see  also 
Blood  flukes. 
hcematohium,    213-217;      distribu- 
tion, 213;   relation  to  host,  214; 
pathogenic  effects,  214;   life  his- 
tory, 215-216;    treatment,  216a; 
mode  of  infection,   216a;    pre- 
vention, 216a-216b. 
japonicum,   215,   218-219;    symp- 
toms of  infection,  218;    life  his- 
tory, 219. 
mansoni,  216,  217-218. 

SCHROEDER,  O.,  6. 
SCHUEFFNER,  W.,  190. 
SCHULZE,  6. 

Schwann,  6. 

Scolex,  231 

Screening,  for  mosquitoes,  457. 

Screw-worm,  see  Cochliomyia  macd- 

laria. 
Scutum,  of  ticks,  354. 
Seal,   host  of  Diphyllohothrium  cor- 

datus,  247. 
Seattle,  plague  in,  411. 
Seed  ticks,  355. 
Seidelin,  H.,  184. 
Sellards,  a.  W.,  136. 
Serbia,  relapsing  fever,  45,  378,  399; 

typhus,  398. 
Sergent,  E.,  471. 
Sesarma  dehaani,  intermediate   host 

of  lung  flukes,  222. 


INDEX 


565 


Seven-day  fever,  Japanese,  73d. 

Seven-days'  fever,  see  Dengue. 

Shanghai,    Clonorchis   sinensis,    225. 

Shaohing,  Fasciolopsis  infections, 
229-230. 

Sheep,  hver  fluke,  209-211;  Param- 
phistomum  cervi,  229;  hydatids, 
248;  host  of  Trichostrongylus  in- 
stabilis,  282;  Ldnguatula  rhina- 
ria,  349;  tick  paralysis,  358- 
359;  grazing  to  destroy  ticks, 
369;  head  maggot,  523. 

Shipley,  A.  E.,  204. 

Shrimp,  host  of  Fasciolopsis  bitsM, 
229. 

Siberia,  Opisthorchis  felineus  in  man, 
225. 

Sicily,  breeding  places  of  phleboto- 
mus  flies,  468,  473. 

SiKORA,  H.,  391,  392,  393,  394. 

Silver,  organic  compounds  of,  for 
Balantidium  infections,  127. 

Silver  nitrate,  for  Vincent's  angina 
and  noma,  73b. 

Simuliidae,  478-484. 

Simulium,  481;    relation  to  Oncho- 
cerca ccBcutiens,  311. 
columba^zense,  482. 
griseicollis,  482. 
pecuarum,  481. 
venustum,  481. 

Siphonaptera,  characteristics,  330, 
404;  see  also  fleas. 

Siphunculata,  330,  388. 

Situtunga  antelope,  reservoir  for 
sleeping  sickness  trypanosomes, 
107;  host  of  Glossina  palpalis, 
498,  499. 

Skunk,  host  of  Pidex  irritans,  414. 

Sleeping  sickness,  importance,  93; 
Rhodesian,  94,  97,  103;  Gam- 
bian,  97,  103;  Nigerian,  98,  103, 
104;  98-108;  transmission,  98- 
99,  490,  496-501;  course  of,  103- 
104;  treatment,  104-106;  pre- 
vention, 106-108;  animal  reser- 
voirs, 107,  503-504. 

Smallpox,  169;  parasite  of,  170,  191. 


Smith,  A.  J.,  142. 

Smith,  J.  B.,  434,  435,  441,  456,  459. 

Smudge,  for  mosquitoes,  457;  for 
blackflies,  484. 

Snails,  intermediate  hosts  of  flukes, 
209-210;  destruction  of,  212; 
of  Schistosoma,  214,  215,  216, 
217,  219-220. 

Snakes,  possible  reservoirs  of  Ldsh- 
mania,  92,  471. 

Snijders,  E.  p.,  173. 

Snow,  F.  H.,  521. 

Snow,  W.  F.,  58. 

Soap,  in  treatment  of  itch,  345. 

Sodium  fluoride,  for  fleas,  421-422. 

Somaliland,  relapsing  fever,  44. 

Sources  of  Information,  periodicals, 
529-531;  books,  531-533. 

South  Africa,  blood-fluke  infections 
in  British  soldiers,  214-215;  in- 
termediate host  of  Schistos- 
oma hcematobium,  216. 

South  America,  oriental  sore,  85; 
uta,  86;  espundia,  89;  trypanoso- 
miasis (Chagas'  disease),  94,  108; 
Cocddium  seeberi,  174;  dengue, 
182;  use  of  shoes,  265;  Filaria 
Persians,  308;  Filaria  juncea, 
308;  land-leeches,  319;  Cimex 
hemipterus,  373;  Triatoma, 
379-381;  Rhodnius  prolixus, 
382;  Dysodius  lunatus,  382- 
383;  Dermatobia  in  cattle,  513. 

South  Sea  Islands,  dengue,  182;  Fil- 
aria bancrofti,  301;  prevalence 
of  elephantiasis,  305;  Aedes  col- 
opus,  448. 

Spagnolio,  G.,  83. 

Spallanzani,  a.,  6. 

Sparganum,  247;  261-263. 
mansoni,  262. 
proliferum,  262-263. 

Spinose  ear  tick,  see  Otiobius 
megnini. 

Spiny-headed  worms,  see  Acantho- 
cephala. 

Spiracles,  of  insects,  328;  of  ticks, 
354. 


566 


INDEX 


Spirochceta,  see  Spirochaetes. 

balanitidis,  41. 

bronchialis,  transmission,  40,  41; 
cause  of  bronchitis,  73b. 

huccalis,  40;  pathogenicity,  73a- 
73b. 

carteri,  42;  in  bedbugs,  378. 

dentium,  40. 

duttoni,  42. 

hebdomadis,  73d. 

icterohcemorrhagioB,  41;  see  also 
under  Leptospira. 

ideroides,  see  under  Leptospira. 

morsus  muris,  73. 

nodosa,  see  Leptospira  ictero- 
hoBmorrhagioe. 

novyi,  42. 

obermeieri,  see  Sp.  recurrentis. 

orientalis,  41. 

pallida,  discovery,  7,   41,  49,  52. 

pertenuis,  41,  63. 

recurrentis,  discovery,  7,  43;  de- 
scription, 52;  distribution  in 
body,  52. 

refringens,  52. 

schaudinni,  41,  73c. 

vincenti,  41. 
Spirochaetes,  cultivation,  9;    38-73; 
relationships,     38;      multipHca- 
tion,  39;   granule  shedding,  39; 
and  disease,  40-42,  73;  localiza- 
tion,   41;    and  relapsing  fever, 
42-48;  and  syphilis,  48-62;  and 
yaws,     63-65;      and    infectious 
jaundice,    65-69;     and   rat-bite 
fever,    73-73a;     and    Vincent's 
angina,    73  a;    and  noma,    73a 
and  balanitis,  73a;   and  mal-de 
boca,  73a;   and  bronchitis,  73b 
and  tropical  ulcer,  73c;   and  ul- 
cerating   granuloma,     73c-73d 
transmission  by  ticks,  360. 
Spleen  rate,  and  prevalence  of  ma- 
laria, 161. 
Sporocyst,    of    coccidian,     172;     of 

flukes,  209;  211. 
Sporozoa,  35,  36;    and  human  dis- 
ease, 149,  168. 


Spotted  fever,  relation  of  ticks  to, 
8,  188-189,  361-363;  and  Piro- 
plasmata,  168;  188-189;  dis^ 
tribution,  188;  parasite  of,  188; 
reservoirs,  189. 

Spotted  fever  tick,  see  Dermacentor 
venustus. 

Squirrels,  hosts  of  Moniliformis 
clarki,  285;  hosts  of  immature 
stages  of  Dermacentor  venustus, 
362;  and  plague,  411,  413;  fleas, 
418. 

Stable-flies,  see  Stomoxys. 

Stanley,  and  spread  of  sleeping 
sickness,  93. 

Staten  Island,  reduction  of  malaria, 
166. 

Staubli,  C,  290. 

Stauffacher,  H.,  76,  193. 

Stegomyia,  see  Aedes. 
fasciatus,  see  Aedes  calopus. 

Stephens,  J.  W.  W.,  282. 

Stephensport,  quininization,  164- 
165. 

Sterilization,  of  blood  against  tryp- 
anosomes,  107. 

Stewart,  F.  H.,  274,  275. 

Sticktight  flea,  see  Echidnophaga  gal- 
linacea,  420. 

Stigmal  plates,  of  maggots,  509-510. 

Stiles,  C.  W.,  116,  125,  242,  252, 
254,  266,  296,  297,  400. 

Stokes,  J.  H.,  483. 

Stomoxys,  transmission  of  Trypano- 
soma gambiense,  98,  507;  rela- 
tion to  Onchocerca  volvulus,  311; 
mouthparts,  327,  464,  505; 
transmission  of  anthrax,  -488, 
507;  504-508;  general  descrip- 
tion, 504-505;  life  history,  505- 
506;  and  disease,  507;  control, 
507-508. 
caldtrans,      504;       and     infantile 

paralysis,  507. 
nigra,     and     Trypanosoma     gam- 
biense, 98,  507. 

Streptothrix,  and  rat-bite  fever,  73a. 

Strickland,  C,  409,  410,  417. 


INDEX 


567 


Strong,  R.  P.,  86,  178,  179,  180, 
397. 

Strongyloides  stercoralis,  279-282; 
life  history,  280-281;  symp- 
toms, 281-282. 

Strongylus,  see  Trichostrongylus. 

Sudan,  spirochsDtal  bronchitis,  73b; 
kala-azar,  77;  Simulium,  482; 
tabanids,  487;  methods  of  cap- 
turing tsetse  flies,  503. 

Sulphur,  for  mites,  335,  339,  341, 
346,  348;  for  fumigation,  383, 
386;  for  hce,  401. 

Sulphur  ointment,  for  itch,  346. 

Sulphuric  acid,  for  hydrocyanic  acid 
fumigation,  384. 

Sumatra,  Eimeria  snijderi,  172; 
pseudo-typhus  or  kedani,  190; 
land-leeches,  319,  320. 

SURCONE,  M.  J.,  451. 

Surra,  99,  487. 

Suzuki,  M.,  219. 

Swallows,  bugs  on,  374;  natural 
enemies  of  mosquitoes,  462. 

SWELLENGREBEL,  N.  H.,  417. 

SwEZY,  O.,  120,  132,  141. 

Swift,  H.  F.,  57. 

Swift-EUis  treatment,  for  syphilis 
of  nervous  system,  57. 

Swifts,  natural  enemies  of  mos- 
quitoes, 462. 

Switzerland,  Diphyllobothrium  latus, 
246. 

Syphilis,  importance  of,  3;  history, 
48-49;  prevalence,  49-51;  trans- 
mission, 51-52;  spirochaetes 
of,  52;  course  of,  53-55;  con- 
genital, 53;  malignant,  55; 
diagnosis,  55-56;  treatment, 
56-58;  standard  of  cure,  57- 
58;  prevention,  58-63;  ex- 
clusion from  hospitals,  58;  free 
diagnosis  and  treatment,  59; 
compulsory  notification,  60; 
relation  to  yaws,  63;  possible 
spread  by  bedbugs,  379;  by 
hce.  400. 


Syria,    oriental    sore,    85;     typhus 
epidemic,  398. 

Tabanidse,    and    leishmaniasis,    75, 
488;  and  espundia,  92,  488-489; 
mouthparts,  327,  485;  484-490; 
general  account,   484-486;     life 
history,   486-487;    and  disease, 
487-489;    transmission  of  surra 
and  el  debab,  487;    and  human 
trypanosomiasis,  488;    and  an- 
thrax, 488;  and  loa  worms,  489; 
control,  489-490. 
Tabanus,  486;  trap  for,  490. 
Tabardillo,  see  Typhus  fever. 
Tcenia  africana,  245. 
bremneri,  245. 
confusa,  245. 
philippina,  245. 

saginata,  discovery  of  life  history, 
7;  nutrition  absorbed,  202;  de- 
scription, 239-240;  hfe  history, 
240. 
solium,  240-242;  cysticerus  in 
man,  261. 
Taeniidae,  238;   important  species  of, 

239-245. 
Takaki,  F.,  73. 

Tampan,  see  Ornithodorus  moubata. 
Taniguchi,  T.,  73. 
Tapeworms,  231-253;   general  struc- 
ture,    231-233;      reproduction, 
233-234;    Hfe  history,  234-235; 
damage  to  host,  236-237;   treat- 
ment,   237;     prevention,    237- 
238;    important  species,   Taeni- 
idae,       239-245;         Dibothrio- 
cephalidae,       245-247;        larval 
tapeworms  of  man,  247-253. 
African,  see  Tcenia  africana. 
beef,  see  Taenia  saginata. 
dog,  see  Dipylidium  caninum. 
dwarf,  see  Hymenolepis  nana. 
fish,  see  Diphyllobothrium  latus. 
pork,  see  Tcenia  solium. 
Tarentola  mauritanica,  and  oriental 
spre,  86,  471. 


568 


INDEX 


Tarsonemidae,  333;  337. 
Tartar  emetic,  discovery,  8;  for 
ulcerating  granuloma,  73d;  for 
kala-azar,  81;  for  infantile  kala- 
azar,  84;  for  oriental  sore,  88 
for  espundia,  91-92;  for  tryp 
anosomes  of  sleeping  sickness 
105;  for  Chagas'  disease,  114 
Taute,  M.,  107. 

Teeth,  pyorrhea  cause  of  loss  of,  142, 
amebae  among,  142-144. 

Temperature,  limiting  factor  in  dis- 
tribution of  parasites,  19. 

Tennent,  J.  E.,  319. 

Ternidens  deminutus,  283. 

Tetramitus,  see  Chilomastix. 

Tetranychidse,  333;  340. 

Tetranychus  molestisswius,  341. 
telarius,  341. 

Texas,  Tcenia  confusa,  245,  Spar- 
ganum  mansoni,  252;  Monili- 
formis, 285;  propagation  of  bats 
to  destroy  mosquitoes,  462. 

Texas  fever,  caused  by  Piroplas- 
mata,  168,  180,  360. 

Texas  fever  tick,  see  Margaropus 
annulatus. 

Theileria  tsutsugamushi,  191. 

Theobald,  F.  V.,  437. 

Theze,  J.,  310. 

Thomas,  W.,  8. 

Three-days'  fever,  see  Phlebotomus 
fever. 

Thymol,  discovery,  8;  for  intes- 
tinal flukes,  230;  for  tapeworms, 
237;  danger  from,  237;  for 
hookworms,  263;  for  pin  worms, 
279;  for  microfilariae,  306. 

Thysanura,  direct  life  history,  329. 

Tick-bite  fever,  367. 

Tick  fever,  see  African  relapsing 
fever. 

Tick  paralysis,  358-359. 

Ticks,  and  espundia,  92;  trans- 
mitters of  Piroplasmata,  168, 
181,  360;  and  kedani,  190,  360; 
352-369;  importance,  352;  gen- 
eral anatomy,  352-354;  habits, 


354;  life  history,  355-357; 
effects  of  bites,  357-358;  tick 
paralysis,  358-359;  and  dis- 
ease, 359-360;  and  relapsing 
fever,  discovery,  8;  43-44; 
352;  transmitting  species,  360- 
361;  and  spotted  fever,  dis- 
covery, 8;  transmission,  188- 
189;  352;  transmitting  species, 
361-363;  troublesome  Argasidae 
364-366;  troublesome  Ixodidse, 
366-367;  treatment  of  bites, 
367;  removal,  367;  prevention, 
368-369. 
Tipulidse,  mosquitoes  allied  to,  425. 
Tlalsahuate,  335. 

Tobacco,  for  leeches,   318,  319;    to 
remove    Dermatobia   from    skin, 
515. 
Todd,  J.  L.,  8,  359. 
Toepfer,  187. 
Togoland,    transmitter    of    sleeping 

sickness  in,  500. 
Tongue- worms,  348-351;  general  ac- 
count,  348;    life  history,    348- 
349;  species  found  in  man,  349- 
351. 
Tonkin,  relapsing  fever  epidemic,  47. 
Tonsilitis,  relation  of  Endamoeha  gin- 

givalis  to,  146. 
Torres,  M.,  Ill,  380. 
Tovar,  N.,  451. 
TowNSEND,  C.  H.  T.,  86,  181,  468, 

472,  473. 
Toxascaris  limbata,  282. 
Toxins,  16-17;    from  spores  of  Sar- 
cosporidia,  175;    from  intestinal 
worms,    202-203;     from     tape- 
worms,    236;      from     Diphyllo- 
bothrium  latus,  247;   from  hook- 
worms,  261;    from  maggots  in 
intestine,  527. 
Tracheae,     of    Arachnida,     324;      of 
insects,   325,   328;    of  Acarina, 
332. 
Trachoma,  169;  193. 
Trematoda,       197-198;        see    also 
Flukes. 


INDEX 


569 


Trench  diarrhea,  135. 

Trench  fever,  168,  169,  186,  187-188; 

relation  of  lice  to,  399. 
Treponema    pallida,    see    Spirochceta 

pallida. 
Triatoma,  relation  to  Trypanosoma 
cruzi,  8,  108,  110-112,  380-381; 
houses  proof  against,  114,  370; 
379-382;  habits  and  life  history, 
379. 

chagasi,  infected  with  trypano- 
somes,  381. 

dimidiata,  infected  with  trypano- 
somes,  381. 

geniculata,  and  Trypanosoma  cruzi, 
112,  380-381. 

infestans,  infected  with  trypano- 
somes,  381. 

megista,  and  Trypanosoma  cruzi, 
110-112;  habits  and  life  his- 
tory, 380. 

protracta,  and  Trypanosoma  tria- 
tomce,  112,  379,  381. 

rybrofasdata,  and  Trijpanosoma 
cruzi,  112,  381;  and  kala-azar, 
377,  382;  -possible  carrier  of 
trypanosome  disease  in  Mauri- 
tius and  Reunion,  381. 

sanguisuga,  110,  379. 

sordida,  infected  with  trypano- 
aomes,  381. 

viMiceps,    infected    with    trypano- 
somes,  381. 
Tricercomonas,  122. 
Trichina     worms,     see     TrichineUa 

spiralis. 
TrichineUa  spiralis,  discovery,  7; 
286-297;  history,  286;  preva- 
lence, 286-288;  life  history, 
288-292;  hosts,  288;  repro- 
duction, 289;  distribution  in 
body  of  host,  290;  formation  of 
cysts,  291;  trichiniasis,  292- 
294;  treatment,  294-295;  pre- 
vention, 295-297;  effects  of 
cold  storage  and  heat,  295; 
meat  inspection  for,  295-296. 
Trichiniasis,     prevalence,     286-288; 


course  of,  292-294;    treatment, 
294-295;    prevention,   295-297. 

Trichinosis,  see  Trichiniasis. 

Trichoma,  396. 

Trichomonas,  115;    118-122;    in  va- 
gina, 119;    in  mouth,  119;    de- 
scription,    119;     multipUcatibn 
and  encystment,  120;  pathogen- 
icity,   121;      treatment    of    in- 
fections, 121. 
buccalis,  119. 
hominis,  118-122. 
vaginalis,  119. 

Tnchostrongylus,  282-283. 
instabilis,  282. 
orientalis,  282. 
suhtilis,  see  T.  instabilis. 

Trichuris  trichiura,  276-277. 

Trinidad,     mosquitoes    thought    to 
transmit  Dermatobia,  451. 

Triodontophoru^,  see  Ternidens. 

Trombidiidae,  see  Harvest  mites. 

Trombidium,  and  kedani,  190. 
akamushi,  336. 
holosericeum,  336. 

Tropical  sloughing  phagedaena,  73c. 

Tropical  ulcer.  73c. 

Tropldurus  peruvianus,  host  of  Phle~ 
botomus  verrv^carum,  472. 

Trypanoplasma,  117. 

Trypanosoma,  relation  of  tsetse  flies 
to,  7,  490,  496-497,  500-501; 
cultivation,  9;  immunity  to 
drugs,  34,  105-106;  develop- 
mental stages,  75,  96-97;  93- 
114;  importance,  93-94;  de- 
scription of,  94-95;  hosts,  96; 
identification  of  species,  96- 
97;  species  pathogenic  to  man, 
97;  and  sleeping  sickness,  98- 
108  j  spores,  102;  granule-shed- 
ding 103  agglutination,  103; 
and  Chagas  disease,  108-114; 
and  leeches  317:  carried  by 
Cimex  pipistrelli,  378;  possible 
cause  of  disease  in  Mauritius 
and  Reunion,  381-382. 
hrucd,  relation  to  Rhodesian  sleep- 


570 


INDEX 


ing  sickness,  108,  497. 
cruzi,  relation  of  Triatoma  to,  8, 
108,  380-381;  and  Chagas'  dis- 
ease, 108-114;  distribution,  108; 
human  cycle,  109-110;  life  cycle 
in  Triatoma,  110-113;   other  in- 
termediate hosts,  112,  378;  ver- 
tebrate hosts,  112. 
gambiense,    discovery,    7;     direct 
transmission,    34,    97;     98-108; 
transmission,   98-99,   496;     dis- 
tribution, 98;    life  cycle  in  fly, 
99-101;   life  cycle  in  man,  101- 
103;  spores,  102;    granule-shed- 
ding,   103;     agglutination,    103; 
and  drugs,   105-106;    transmit- 
ting species,   496-501;    relation 
of  stable-flies  to,  98,  507. 
lewisi,  immunity  to  drugs,  105. 
nigeriense,    98;      and    stable-flies, 

98,  507. 
rhodesiense,  97;  distribution,  98; 
and  sleeping  sickness,  98-108; 
pathogenicity  and  relation  to 
T.  brucei,  107-108;  and  drugs, 
106;  transmitting  species,  98, 
497,  499-501. 
triatomce,  112,  381. 

Trypanosome  fever,  103-104. 

Tryparsamide,  for  trypanosomiasis, 
105. 

Tsetse  flies,  relation  to  trypano- 
somes,  7,  98-101,  496-497, 
500-501;  relation  to  Onchocerca 
volvulus,  311;  mouthparts,  327, 
464,  491;  reproduction,  464, 
495;  490-504;  importance, 
490;  general  account,  491-492; 
distribution,  492;  habits,  493- 
495;  life  history,  495-496;  and 
disease,  496-501;  control,  501- 
504. 

Tsutsugamushi,  see  Leptvs  aka- 
mushi  and  Kedani. 

Tuberculosis,  possible  spread  by 
bedbugs,   379. 

Tularemia,  413,  489. 


Tumbu  fly,  see  Cordylohia  anthro- 
pophaga. 

Tunis,  Leishmania  in  gecko,  86. 

Tunnel  disease,  see  Hookworm. 

TUNNICLIFF,  R.,  73a. 

Tuntun,  see  Hookworm.' 

TurbeUaria,  197. 

Turpentine,  to  keep  away  ticks,  368; 
for  bugs,  383;  oil  of,  for  body 
lice,  401;  resistance  of  maggots 
to,  522. 

Tydeus  molestus,  341. 

Typhoid,  relation  of  intestinal  worms 
to,  in  apes,  204. 

Typhus,  168;  organisms  of,  169, 
186-187;  nature  of,  186;  dis- 
covery of  louse  transmission, 
397;  epidemiology,  397-398. 
in  European  War,  2,  398;  relation 
of  lice  to,  8,  397-399;  cause  of, 
73, 169, 195,  397,  epidemics,  398- 
399;  and  fleas,  414. 

Tyroglyphidse,  333;  339-340. 

Tyroglyphus,  340. 
longior,  340. 
longior  castellanii,  340. 

Uganda,  sleeping  sickness,  93;  fish- 
ing industry  and  sleeping  sick- 
ness, 106-107;  Filaria  per- 
stans,  308. 

Ulcerating  granuloma,  73c-73d. 

Undulating  membrane,  30. 

United  States,  plague  in,  2,  411; 
syphilis  in,  .3;  hookworm  in 
immigrants,  5,  268;  amebic 
dysentery,  6,  134  ;  relapsing 
fever,  43;  syphilis,  50;  yellow 
fever,  69-70;  rat-bite  fever,  73; 
possibility  of  kala-azar,  77; 
prevalence  of  intestinal  Proto- 
zoa in  South,  116;  Emhado- 
monas,  118;  Trichomonas  path- 
ogenic, 121;  amebic  dysentery, 
134;  malaria,  147-148,  163; 
black  water  fever,  161;  swamp 
land  and  malaria,  166;    dengue, 


INDEX 


571 


182;  spotted  fever,  188-189; 
possibility  of  introduction  of 
blood  flukes,  220;  Paragonimus 
keUicotti,  220,  223;  Ojristhorchis 
pseudofelineus,  225;  Paramphis- 
tomum  in  cattle,  229;  Toenia  sol- 
ium, 240;  Hymenole-pis  nana, 
242;  Hymenolepis  diminuta,  244; 
Diphyllobothrium  latus,  246;  hy- 
datids, 248;  hookworm,  254, 
255,  262,  263,  268;  privies,  266; 
Moniliformis,  285;  prevalence 
of  trichina  in  hogs,  286,  287; 
prevalence  of  trichina  in  man, 
287;  Filaria  bancrofti,  299; 
red-bugs,  336;  Pediculoides, 
338;  Norwegian  itch,  343;  eco- 
nomic importance  of  ticks, 
352;  tick  paralysis,  358;  Der- 
macentor  venustus,  363;  Otiobius 
megnini,  365;  Triatoma,  379, 
381;  kissing  bugs,  382;  plague- 
like disease  transmitted  by  fleas, 
413;  Pulex  irritans,  415;  Cteno- 
cephalus  canis,  416;  Ceratophyl- 
lus,  418;  Echidnophaga  galli- 
nacea,  420;  Aedes  calopus,  447; 
Cvlex  quinqueja^ciatus,  449; 
mosquito  canopies,  457;  No- 
tophthalmus  torosus  natural  en- 
emy of  mosquitoes,  461;  black- 
flies,  481;  tularemia,  489; 
infantUe  paralysis,  507. 

United  States  Army,  syphilis  in,  50. 

United  States  Bureau  of  Animal 
Industry,  experiments  with  tri- 
china, 295. 

United  States  Bureau  of  Entomol- 
ogy, 508. 

Uranotcenia,  palpi,  426. 

Uruguay,  dengue,  182;  TetranycJius 
molestissimus,  341. 

Uta,  86;  87;  88;  477. 

Vaccination,  4;  broad  meaning  of, 
22;  in  yellow  fever,  72;  in 
treatment  of  hookworm  dis- 
ease, 263. 


Vaccine  or  cowpox,  191. 

Vahlkampfia,  132. 

Van  den  Branden,  F.,  107. 

Vaullegeard,  a.,  202. 

Vedder,  E.  B.,  8,  50. 

Venezuela,  Schistosoma  manaoni, 
217;  Rhodnius  prolixus,  382; 
Dermatobia  carrier,  452. 

Vera  Cruz,  amebic  dysentery,  139; 
malaria,  166. 

Ver-du-cayor,  see  Cordylobia  anthro- 
pophaga. 

Vermes,  196. 

Verruga  peruviana,  169,  193;  rela- 
tion to  Oroya  fever,  178,  195; 
and  Phlebotomus  verrucarum, 
472. 

Vespa  macvlata,  natural  enemy  of 
tabanids,  490. 

ViANNA,  G.,  8,  73d,  81,  109. 

Vincent's  angina,  cause  of,  73a; 
treatment,  73b. 

Vinchuca,  see  Triatoma  infestans. 

Vinegar,  efifect  on  Clonorchis  cer- 
cariae,  227;  and  kerosene  for 
lice,  402;  repellent  for  mos- 
quitoes, 455. 

Volhynian  fever,  187. 

VON  DuscH,  6. 

Von  Ezdorf,  H.,  148. 

VoN  Linstow,  see  Linstow,  von. 

Walker,  E.  L.,  136,  138,  139. 

Wallace,  A.,  320. 

Walsh,  B.  D.,  524. 

Warbles,  see  Hypoderma. 

Ward,  H.  B.,  245,  285. 

Wart  hog,  host  of  Choeromyia,  512. 

Washington,  D.  C,  dispersal  of  hce 
in  family  wash,  401;  developn 
ment  of  Anopheles  quadrimxicu- 
latus,  442. 

Waskia,  see  Embadomonas. 

Wassermann,  a.  von,  49. 

Wassermann  reaction  49;  50;  66-56. 

Water-dogs,  natural  enemies  of  mos- 
quitoes, 461. 

Watsonius  watsoni,  229. 


572 


INDEX 


Weil's  Disease,  see  Infectious  jaun- 
dice. 

Weinberg,  M.,  204. 

Weinland,  D.  F.,  7. 

Wenyon,  C.  M.,  85,  118,  121,  123, 
124,  125,  156,  172,  173,  471. 

Western  Australia,  compulsory  noti- 
fication of  syphilis,  60. 

West  Indies,  dengue,  182;  Schisto- 
soma mansoni,  217;  hookworm 
disease,  264;  Necator  americanus, 
255;  work  of  Hookworm  Com- 
mission, 268;  Filaria  per  starts, 
308;  bete  rouge,  335;  Cimex 
hemipteruSf  373;  chigger,  419, 
origin  of  yellow  fever,  447; 
home  of  "millions,"  461. 

West  Point,  syphilis  at,  51. 

Whipworm,  see  Trichuris  trichiura. 

Whitmarsh,  p.  L.,  305. 

Wilder,  R.  M.,  8,  397. 

Wild  game,  extermination  to  eradi- 
cate sleeping  sickness,  107;  and 
control  of  spotted  fever  in  Uni- 
ted States,  189;  hosts  of  Der- 
macentor  venustus,  363;  hosts 
of  tsetse  flies,  490,  498. 

Williams,  Anna,  143,  193. 

Wohlfartia  magnifica,  521-522. 

WOLBACH,  S.  B.,  188. 

Woodrats,  host  of  Triatoma  pro- 
tracta,  112. 

Woodtick,  see  Dermacentor. 

Worcester,  D.  C,  320. 

Worms,  196-205;  classification,  196; 
flat  worms  in  general,  196-198; 
roundworms  in  general,  198-199; 
annelids  in  general,  199-200; 
parasitic  habitats,  200;  life 
history  and  modes  of  infection, 
200-201;  effects  of  parasitism, 
201-204;  nutriment  absorbed, 
202;  toxic  effects,  202;  infection 
of  wounds  made  by,  204;  rela- 
tion to  appendicitis,  204;  diag- 
nosis,   204-206;     eggs   of,    205. 


See  also  Intestinal  worms  and 

various  species. 
Wrigglers,  431. 
Wright,  R.  E.,  306. 
Wyeomyia  smithii,  hibernation,  436. 
Xanthium    macrocarpum,    mites    on 

leaves  of,  341. 
Xenopsylla     cheopis,     identification, 

408;     and    plague,     411,     412; 

intermediate   host  of  Hymeno 

lepis,   414;     distinguished  fron 

Pulex  irritans,  415;  habits,  etc. 

417. 
X-ray,  for  ulcerating  granuloma,  73d 

Yakimoff,  W.  L.,  377. 

Yaws,  63-65;  distribution,  63;  spire 

chsetes   of,    63;     course   of,    6.' 

treatment,    64-65;     preventioi; 

65. 
Yellow  fever,  69-72;  in  Panama,  2 

relation  of  mosquitoes  to,  7,  44o 

parasite  of,   70,    169;    distribu 

tion,     69-70;      course    of,     71; 

treatment  and  prevention,   71- 

72;       transmitting      mosquito, 

443-448. 
Yellow  fever  group  of  parasites,  169, 

182. 
Yellow   fever   mosquito,    see   Aedes 

calopus. 
Yersin,  a.,  411. 
Yokagawa  yokagawa  (Metagonimus), 

intermediate  host,  226;   228. 
Yorke,  W.,  100,  494,  496. 
YosHiDA,  S.,  222,  223. 
Yquitos,  reduction  of  yellow  fever, 

72. 
Yucatan,  yellow  fever  in,  70. 

Zambezi,  danger  of  spread  of  Glos- 

sina  palpalis  to,  498. 
Zebu,  possible  intermediate  host  of 

Twnia  africana,  245. 
Zenker,  F.  A.  von,  7. 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


RENEWED  BOOKS  ARE  SUBJECT  TO  IMMEDIATE 
RECALL 


mwm* 


^  JUN  a  9  1982 


AUG  IG  19 cJ 


r—  RtrsLED  HSL 

AUG  0  7  1930 


LIBRARY,  UNIVERSITY  OF  CALIFORNIA,  DAVIS 

Book  Slip-25m-6,'66(G3855s4)458 


3  1175  00627  0998 


PEPARTMT5N'' 


Boo« 


OAKD 


QXU 


^23 

/9ZZ 

S^icl    hur^an    ^z-^^^^^' 

HEALT-, 
SCIENCES 

UBRARV 

